[Differential diagnosis and management of hemangioma at geniculate ganglion].

Objective: To investigate the clinical characteristics, differential diagnosis, treatments and prognosis of facial nerve hemangioma and schwannoma at genicular ganglion, so as to provide reference for clinical diagnosis and treatments of facial nerve tumor at genicular ganglion. Methods: Clinical data of 13 patients with facial nerve tumors at genicular ganglion confirmed by postoperative pathology in the Ninth People's Hospital affiliated to Shanghai Jiaotong University School of Medicine from March 2018 to April 2020 were retrospectively analyzed, including seven cases of hemangioma and six cases of schwannoma. There were eight males and five females. Their ages ranged from 20 to 65, with an average age of 40. The course of disease ranged from 3 to 118 months, with an average of 52 months. All the patients underwent preoperative HRCT of the temporal bone and facial nerve dynamic contrast-enhanced(DCE) MRI examinations. All the patients had detailed surgical procedures and at least one-year postoperative follow-up. Results: On HRCT of the temporal bone, (4/7) hemangioma at geniculate ganglion showed characteristic honeycomb appearance, while 6/6 schwannoma and 3/7 hemangiomas showed expansive bone changes. On DCE-MRI, geniculate ganglion hemangioma (7/7) showed characteristic "point-to-surface" enhancement, and schwannoma (6/6) showed characteristic "face-to-surface" enhancement. For five hemangioma-patients with HB-Ⅱ-Ⅳ before surgery, the facial nerve anatomy was completely preserved through transcanal endoscopic approach(TEA), and the facial nerve function improved one year after surgery (two cases of HB-I, two cases of HB-Ⅱ, and one case of HB-Ⅲ). For two patients, with preoperative facial nerve function HB-Ⅴ-Ⅵ, since their tumors was inseparable from the nerves, they were performed with facial nerve anastomosis during the surgery, and the facial nerve function was improved to HB-Ⅳ level one year after surgery. For six patients with meningioma whose facial nerve function was greater than or equal to HB-Ⅲ, based on the preoperative hearing level, the involved segments, and duration of facial paralysis, three of them were conducted surgeries through middle cranial fossa approach, one by translabyrinthine approach, and one via mastoid approach. Two patients among them with complete facial paralysis over three years preoperatively were not performed facial nerve anastomosis after total resections of the tumors, and there was no improvement in facial nerve function one year after surgery. Three patients underwent facial nerve anastomosis after total tumor resections, and their facial nerve function was HB-Ⅲ in one patient, HB-Ⅳ in two patients one year after surgery. One patient (preoperative HB-Ⅲ) had a normal hearing level preoperatively, and the tumor involved the labyrinth segment. To protect the hearing, partial tumor was resected through the middle cranial fossa approach, and facial nerve function improved to HB-Ⅱ one year after surgery. Conclusions: Temporal bone HRCT combined with DCE-MRI are useful for the differential diagnosis of hemangioma and schwannoma at geniculate ganglion and provide references for preoperative clinical decision makings. It is extremely necessary to select the appropriate surgical approach based on the patient's hearing and involved segments. For geniculate ganglion hemangioma, early surgery can improve the possibilities of anatomical integrity of facial nerve, thereby improving facial nerve function postoperatively.TEA is a kind of surgical method worth consideration, with the characteristics of minimally invasive, favorable postoperative features, and so on. For schwannoma, one-stage functional reconstruction of the facial nerve is recommended during the resection of the tumors because of the inevitable damage to the anatomical integrity of the facial nerve.

Causal somatic mutations in urine DNA from persons with the CLOVES subgroup of the PIK3CA-related overgrowth spectrum.

Congenital lipomatous overgrowth with vascular, epidermal, and skeletal (CLOVES) anomalies and Klippel-Trenaunay (KTS) syndromes are caused by somatic gain-of-function mutations in PIK3CA, encoding a catalytic subunit of phosphoinositide 3-kinase. Affected tissue is needed to find mutations, as mutant alleles are not detectable in blood. Because some patients with CLOVES develop Wilms tumor, we tested urine as a source of DNA for mutation detection. We extracted DNA from the urine of 17 and 24 individuals with CLOVES and KTS, respectively, and screened 5 common PIK3CA mutation hotspots using droplet digital polymerase chain reaction. Six of 17 CLOVES participants (35%) had mutant PIK3CA alleles in urine. Among 8 individuals in whom a mutation had been previously identified in affected tissue, 4 had the same mutant allele in the urine. One study participant with CLOVES had been treated for Wilms tumor. We detected the same PIK3CA mutation in her affected tissue, urine, and tumor, indicating Wilms tumors probably arise from PIK3CA mutant cells in patients with CLOVES. No urine sample from a participant with KTS had detectable PIK3CA mutations. We suggest that urine, which has the advantage of being collected non-invasively, is useful when searching for mutations in individuals with CLOVES syndrome.

Confocal imaging of mouse mandibular condyle cartilage.

Mice are commonly used to study the temporomandibular joint (TMJ) and to model human TMJ disease. However, evaluating TMJ pathology in mice using standard histologic methods is time consuming, labor intensive, and dependent upon investigators' expertise at consistently orienting and sectioning across tiny specimens. We describe a method that uses confocal microscopy to rapidly and reliably assess indicators of mandibular condyle cartilage pathology in mice. We demonstrate the utility of this method for detecting abnormalities in chondrocyte distribution in mice lacking lubricin (Prg4), the major boundary lubricant of articular cartilage. We further show that the method can provide information about recombination sites and efficiency in mandibular cartilage for Cre-driver strains. Because specimen preparation and data acquisition with confocal microscopy are simple and fast, the method can serve as a primary screening tool for TMJ pathology, before proceeding to complicated, time consuming, secondary analyses.

Resting (basal) secretion of proteins is provided by the minor regulated and constitutive-like pathways and not granule exocytosis in parotid acinar cells.

Resting secretion of salivary proteins by the parotid gland is sustained in situ between periods of eating by parasympathetic stimulation and has been assumed to involve low level granule exocytosis. By using parotid lobules from ad libitum fed rats stimulated with low doses of carbachol as an in vitro analog of resting secretion, we deduce from the composition of discharged proteins that secretion does not involve granule exocytosis. Rather, it derives from two other acinar export routes, the constitutive-like (stimulus-independent) pathway and the minor regulated pathway, which responds to low doses of cholinergic or beta-adrenergic agonists (Castle, J. D., and Castle, A. M. (1996) J. Cell Sci. 109, 2591-2599). The protein composition collected in vitro mimics that collected from cannulated ducts of glands given low level stimulation in situ. Analysis of secretory trafficking along the two pathways of resting secretion has indicated that the constitutive-like pathway may pass through endosomes after diverging from the minor regulated pathway at a brefeldin A-sensitive branch point. The branch point is deduced to be distal to a common vesicular budding event by which both pathways originate from immature granules. Detectable perturbation of neither pathway in lobules was observed by wortmannin addition, and neither serves as a significant export route for lysosomal procathepsin B. These findings show that parotid acinar cells use low capacity, high sensitivity secretory pathways for resting secretion and reserve granule exocytosis, a high capacity, low sensitivity pathway, for massive salivary protein export during meals. An analogous strategy may be employed in other secretory cell types.

Relative frequencies of DRB1*11 alleles and their DRB3 associations in five major population groups in a United States bone marrow registry.

One hundred sixty-one individuals from each of five US population groups, Caucasians (CAU), African Americans (AFA), Asians/Pacific Islanders (API), Hispanics (HIS), and Native Americans (NAT), were randomly selected from a volunteer bone marrow registry database consisting of 14,452 HLA-DRB1*11 positive individuals. This sampling provided at least an 80% probability of detecting a rare allele that occurred at 1% in the DRB1*11 positive population. Samples were typed for DRB1*11 alleles by polymerase chain reaction-sequence specific oligonucleotide probe typing (PCR-SSOP). A total of 10 DRB1*11 alleles out of 27 possible alleles were detected. The distribution and diversity of DRB1*11 alleles varied among populations although DRB1*1101 was the predominant DRB1*11 allele in all populations. Caucasians were the least diversified; only four common alleles (DRB1*1101-*1104) were observed. As well as the four common alleles, other groups also carried one or two other less frequent alleles including DRB1*1105 (API), *1106 (API), *1110 (AFA), *1114 (HIS), *1115 (NAT), and *1117 (AFA). A subset (418) of these individuals were also typed for DRB3 alleles. Most (97.6%) showed a strong association of DRB1*11 with DRB3*0202.

Antigen-specific cancer immunotherapy using a GM-CSF secreting allogeneic tumor cell-based vaccine.

Granulocyte-macrophage colony-stimulating factor (GM-CSF)-transduced autologous tumor cell-based vaccines are currently one of the major forms of cancer vaccines. However, the preparation of GM-CSF-transduced autologous tumor vaccines is time-consuming and technically challenging. In addition, the host antigen presenting cells, rather than the tumor vaccine cells themselves, present tumor-specific antigens and prime the host T cells. Therefore, we tested the efficacy of antigen-specific allogeneic tumor vaccines. We used human papillomavirus 16 (HPV-16) E7 protein as a model tumor antigen, which is associated with the development of most cervical carcinoma. B16, a C57BL/6 (H-2(b)) derived melanoma cell line, was genetically engineered to produce GM-CSF alone (B16GM), HPV-16 E7 alone (B16E7), or both (B16GME7). These vaccine cells were injected into BALB/c (H-2(d)) mice (10(6) cells/mouse). Two weeks later, mice were challenged with 10(5) live HPV-16 E7(+) BL-1 (H-2(d)) tumor cells and monitored for tumor progression twice weekly. To determine the effective cell population in the antitumor immunity elicited by B16GME7, we carried out in vivo antibody depletion experiments using CD4 and CD8 specific antibodies. In addition, as a measure of the immune responses produced by B16GME7, we performed an in vitro cytotoxic T lymphocyte assay using a standard chromium release method. We found that all of the mice vaccinated with B16GME7 remained tumor free 49 days post-BL-1 challenge. In contrast, mice vaccinated with B16GM and B16E7 did not show any tumor protection against a similar dose of BL-1 cells. Furthermore, the antitumor immunity produced by B16GME7 was dependent on both CD4 and CD8 T cells. In addition, E7-specific cytotoxic T lymphocyte activity could be readily demonstrated in mice immunized with B16GME7. These results suggest that allogeneic tumor cells transduced with GM-CSF and the tumor antigen, HPV-16 E7, cannot only generate an E7-specific cytotoxic T lymphocytes response in vitro, but can also elicit a potent antitumor immune response against an E7 expressing tumor in vivo.

Functional volumes modeling: scaling for group size in averaged images.

Functional volumes modeling (FVM) is a statistical construct for metanalytic modeling of the locations of brain functional areas as spatial probability distributions. FV models have a variety of applications, in particular, to serve as spatially explicit predictions of the Talairach-space locations of functional activations, thereby allowing voxel-based analyses to be hypothesis testing rather than hypothesis generating. As image averaging is often applied in the analysis of functional images, an important feature of FVM is that a model can be scaled to accommodate any degree of intersubject image averaging in the data set to which the model is applied. In this report, the group-size scaling properties of FVM were tested. This was done by: (1) scaling a previously constructed FV model of the mouth representation of primary motor cortex (M1-mouth) to accommodate various degrees of averaging (number of subjects per image = n = 1, 2, 5, 10), and (2) comparing FVM-predicted spatial probability contours to location-distributions observed in averaged images of varying n composed from randomly sampling a 30-subject validation data set.

Dodecafluoropentane ultrasonic contrast enhancement in carotid diagnosis: preliminary results.

To assess the efficacy in carotid diagnosis of an investigational dodecafluoropentane ultrasonic contrast enhancing agent, we compared B-mode, color flow, and duplex Doppler findings in 16 patients with common carotid artery bifurcation disease after dodecafluoropentane and saline injections. Dodecafluoropentane produced enhanced backscatter in all patients for 4 to 20 min (mean, 8.4+/-4.74 min) after intravenous injection. In six patients this enhancement improved the color flow and pulsed Doppler signal detection in areas of sonographic shadowing. The enhanced color flow information changed the diagnostic impression in one case. Dodecafluoropentane produced enhanced backscatter in the carotid artery in all patients, and for a mean duration longer than that reported for other agents. It has the potential to improve the efficacy of carotid ultrasonic evaluation.

Immunoglobulin-derived polypeptides enter the regulated secretory pathway in AtT-20 cells.

Constitutively secreted proteins have traditionally been believed to be excluded from the regulated secretory pathway. In this work we show that kappa light chain and Fc fragment, two markers of the constitutive pathway, are present in the regulated pathway in AtT-20 cells. They colocalize with the endogenous hormone ACTH and they exhibit stimulus-dependent secretion. The Fc fragment, which undergoes intracellular transport at the same rate as the ACTH precursor POMC, enters the forming secretory granules, however, it is partially lost during granule maturation. These observations show that classic constitutive secretory markers are not excluded from the regulated secretory pathway and that efficient sorting for regulated secretion occurs above a background of proteins which enter the granules without sorting.

Passive sorting in maturing granules of AtT-20 cells: the entry and exit of salivary amylase and proline-rich protein.

Previous studies have suggested that salivary amylase and proline-rich protein are sorted differently when expressed in AtT-20 cells (Castle, A.M., L.E. Stahl, and J.D. Castle. 1992. J. Biol. Chem. 267:13093- 13100; Colomer, V., K. Lal, T.C. Hoops, and M.J. Rindler. 1994.EMBO (Eur. Mol. Biol. Organ.) J. 13:3711- 3719). We now show that both exocrine proteins behave similarly and enter the regulated secretory pathway as judged by immunolocalization and secretagogue- dependent stimulation of secretion. Analysis of stimulated secretion of newly synthesized proline-rich protein, amylase, and endogenous hormones indicates that the exogenous proteins enter the granule pool with about the same efficiency as the endogenous hormones. However, in contrast to the endogenous hormones, proline-rich protein and amylase are progressively removed from the granule pool during the process of granule maturation such that only small portions remain in mature granules where they colocalize with the stored hormones. The exogenous proteins that are not stored are recovered from the incubation medium and are presumed to have undergone constitutive-like secretion. These results point to a level of sorting for regulated secretion after entry of proteins into forming granules and indicate that retention is essential for efficient storage. Consequently, the critical role of putative sorting receptors for regulated secretion may be in retention rather than in granule entry.

Spectral cues for sound localization in cats: a model for discharge rate representations in the auditory nerve.

Neural representations of pinna-based spectral cues for sound localization were modeled by simulating auditory nerve discharge rates to noise bursts that had been shaped by filtering properties of the cat's head-related transfer functions (HRTFs) at 179 locations in the frontal field. The auditory nerve model transformed spectral differences between HRTFs into simulated neural rate differences. Linear equations for this transformation were developed from actual auditory nerve responses to a limited subset of HRTF-filtered noise bursts [Rice et al., J. Acoust. Soc. Am. 97, 1764-1776 (1995)]. Signal detection methods were used to investigate simulated neural responses to pairwise changes between HRTFs. The quality of neural representation for these changes, in terms of d' values, declined when the reference HRTF was moved from a central location (0 degree AZ, 0 degree EL) to a large positive azimuth in the horizontal plane (75 degrees AZ, 0 degree EL) or a high elevation in the median plane (0 degree AZ, 75 degrees EL). Most simulated responses exhibited large d' values for comparisons of contralateral versus ipsilateral azimuths, or eccentric versus frontal elevations. This rate information resulted from directionally dependent changes in the overall gain of HRTFs. In addition, fibers with best frequency (BF: the frequency of greatest sensitivity for individual fibers) between 5 and 18 kHz showed large d' values for HRTF contrasts in the immediate frontal field because of the effects of spectral notches (i.e., sharp drops in gain over a narrow frequency range). Spectral notches also played a prominent role in simulations that required identification of HRTF location in the absence of a fixed reference stimulus. These modeling results correspond well with previously described patterns in the cat's localization behaviors.

Frequency-selective fat suppression MR imaging. Localized asymmetric failure of fat suppression mimicking orbital disease.

Our objectives were to further characterize an artifact related to the localized failure of the frequency-selective (FATSAT) fat suppression magnetic resonance (MR) imaging technique. We constructed two phantoms simulating human orbital anatomy and imaged them on a 1.5-T MR scanner using (FATSAT) and short T1 inversion recovery (STIR) techniques of fat suppression. The first phantom resembled orbit structural configurations; it was imaged in coronal and axial planes and in varying orientations with respect to the main magnetic field (Z axis) to study the features of the artifact and to reproduce the asymmetry seen in clinical cases. We designed the second phantom to enable quantification of the change in artifact size with change in orientation. We imaged the orbits of a normal human volunteer in similar planes and orientations, and compared the results to clinical cases demonstrating the artifact and true orbital disease. The artifact identified with localized failure of FATSAT fat suppression manifested as regions of hyperintensity maximal at fat-air interfaces, with gradual fading of the increased signal with distance from the interfaces. The artifact was most prominent when the interfaces were perpendicular to the axis of the main magnetic field (Z axis). The regions of increased brightness obscured normal orbital structures but were not associated with alterations in the geometry of these structures. Changes in orientation of the interfaces with respect to the Z axis, both in the phantoms and normal volunteer, reproduced the asymmetry of fat suppression failure seen in clinical cases. The relationship of size of the artifact to change in orientation was non-linear. The artifact was not seen on STIR images. We concluded that failure of FATSAT fat suppression may mimic orbital disease, particularly if asymmetric. As predicted by the Maxwell electromagnetism equation, slight variations in orientation of the fat-air interface to the Z axis may produce large asymmetries in fat suppression failure in the orbit. Confirmation may require either comparison with additional pulse sequences [T1-weighted spin echo (T1W SE) or STIR] or repositioning the patient's head to check for persistence of the finding with varying orientations.

Spectral cues for sound localization in cats: effects of frequency domain on minimum audible angles in the median and horizontal planes.

Rice et al. [Hear. Res. 58, 132-152 (1992)] classified directional properties of the cat's head-related transfer function (HRTF) into three frequency domains. Low frequencies (< 5 kHz) display a broad azimuth-sensitive spectral peak that establishes interaural level differences, mid frequencies (5-18 kHz) are marked with a single deep spectral notch that changes in frequency as a function of both azimuth and elevation, and high frequencies (18-50 kHz) exhibit a complex pattern of peaks and notches that shows extensive but less systematic changes with sound location. Spectral cues conveyed by the mid frequencies of broadband sounds are important in tasks that require cats to identify the actual location of acoustic stimuli [Huang and May, J. Acoust. Soc. Am. (in press)]. The present study investigates how directional cues conveyed by the mid- and high-frequency spectrum of the HRTF influence the cat's ability to discriminate between sound locations. Thresholds for spatial acuity were measured as minimum audible angles (MAAs) [Mills, J. Acoust. Soc. Am. 30, 237-246 (1958)] at positive azimuths in the interaural horizontal plane and at positive and negative elevations in the median vertical plane. The frequency domain of the noise burst had little effect on MAAs in the horizontal plane, but removal of high-frequency spectral information significantly increased thresholds at positive and negative elevations in the median plane. These results suggest that cats are sensitive to directional properties of the HRTF at frequencies above 18 kHz and may use this information to detect small changes in sound source elevation.

The immunodominant major histocompatibility complex class I-restricted antigen of a murine colon tumor derives from an endogenous retroviral gene product.

Tumors express peptide antigens capable of being recognized by tumor-specific cytotoxic T lymphocytes (CTL). Immunization of mice with a carcinogen-induced colorectal tumor, CT26, engineered to secrete granulocyte/macrophage colony-stimulating factor, routinely generated both short-term and long-term CTL lines that not only lysed the parental tumor in vitro, but also cured mice of established tumor following adoptive transfer in vivo. When either short-term or long-term CTL lines were used to screen peptides isolated from CT26, one reverse-phase high performance liquid chromatography peptide fraction consistently sensitized a surrogate target for specific lysis. The bioactivity remained localized within one fraction following multiple purification procedures, indicating that virtually all of the CT26-specific CTL recognized a single peptide. This result contrasts with other tumor systems, where multiple bioactive peptide fractions have been detected. The bioactive peptide was identified as a nonmutated nonamer derived from the envelope protein (gp70) of an endogenous ecotropic murine leukemia provirus. Adoptive transfer with CTL lines specific for this antigen demonstrated that this epitope represents a potent tumor rejection antigen. The selective expression of this antigen in multiple non-viral-induced tumors provides evidence for a unique class of shared immunodominant tumor associated antigens as targets for antitumor immunity.

Sound orientation behavior in cats. I. Localization of broadband noise.

Behavioral experiments measured the accuracy of the cat's voluntary head orientation responses to bursts of broadband noise at 104 locations in the frontal sound field. Cats were presented sound stimuli at randomly selected locations and received a food reward for releasing a lever when a light-emitting diode (LED) flashed at the same location. Head movements to the perceived location of the acoustic stimulus, and therefore expected location of the LED cue, were tracked by an electromagnetic sensor. Orientation responses to single sound bursts were directed to within 5 degrees of the azimuth and elevation of sounds within 15 degrees of the immediate frontal field and did not change for burst durations of 40, 100, and 200 ms. An increasing underestimation of target location was observed as the sound stimulus moved to more lateral azimuths and higher elevations. The "undershoot" phenomenon was reduced by allowing subjects to track paired stimulus bursts that repeated from the same location. These effects of sound location on the accuracy of orientation responses are predicted by the availability of mid-frequency spectral cues for sound localization.

Sound orientation behavior in cats. II. Mid-frequency spectral cues for sound localization.

The cat's head-related transfer function creates a directionally dependent mid-frequency notch in the amplitude spectrum of a broadband sound as the stimulus propagates to the tympanic membrane [Rice et al., Hear. Res. 58, 132-152 (1992)]. Our previous behavioral studies [May and Huang, J. Acoust. Soc. Am. 100, 1059-1069 (1996)] have indicated that the cat's sound-evoked orientation responses are well directed to the azimuth and elevation of broadband noise bursts in the frontal sound field, where pinna-based spectral notches are prominent and change systematically with sound direction. In the present study, the importance of mid-frequency directional cues in the cat's sound localization behavior was further evaluated by manipulating the frequency and bandwidth of orientation stimuli. The accurate pattern of orientation behavior seen previously with bursts of broadband noise was relatively unaffected when stimulus bandwidth was decreased to mid-frequency bandpass noise of 5-18 kHz. In contrast, poorly directed head orientation responses were observed in tests with high-pass noise (> 18 kHz) and mid-frequency pure tones. When tested with narrow bands of mid-frequency noise, cats oriented toward the spatial location where HRTF-filtering properties most closely matched the stimulus spectrum. These results suggest that important sound localization cues are derived from mid-frequency spectral features of the cat's HRTF.

Enhanced immune priming with spatial distribution of paracrine cytokine vaccines.

In preclinical models, tumor cells genetically modified to express cytokines or other costimulatory molecules can generate systemic antitumor immunity. In some cases, these tumor vaccines have been shown to eradicate micrometastases. These results have led to the initiation of numerous phase I clinical trials employing either autologous or allogeneic tumor vaccines genetically modified to express cytokines and other genes. In this report, we use our murine model to identify a number of parameters that may be critical for enhancing vaccine efficacy. In addition to antigen dose and cytokine level, the distribution of vaccine inoculation was found to have a significant impact on vaccine potency. These results require consideration in early clinical trials designed to evaluate cellular vaccine therapy.

In vivo cross-priming of MHC class I-restricted antigens requires the TAP transporter.

Recent in vitro evidence suggests two alternative mechanisms by which bone marrow-derived APCs may process exogenous antigens for presentation to CTL in vivo, a phenomenon termed cross-priming. Although in vitro studies have suggested that both TAP-dependent and TAP-independent pathways exist, we have now demonstrated an absolute requirement for a functional TAP for cross-priming to occur in vivo. Bone marrow chimeras reconstituted with marrow from TAP-defective donors develop functional CD8+ CTL, but have APCs with disrupted TAP function. In such chimeras, in vivo priming of naive CTL was observed when antigen was targeted to the ER in a TAP-independent fashion, but cross-priming could not be demonstrated. These results support the TAP-dependent mechanism of cross-priming.

Does B7-1 expression confer antigen-presenting cell capacity to tumors in vivo?

Tumors engineered to express the costimulatory molecule B7-1 can elicit CD8+ cytotoxic T lymphocyte (CTL)-dependent antitumor responses in immunocompetent mice. It has been postulated that this result reflects direct priming of CTL by the modified tumor in vivo. Previous studies of the immune response to a B7-1- murine colon carcinoma expressing influenza nucleoprotein (NP) as a model tumor antigen have demonstrated the crucial role of bone marrow-derived antigen-presenting cells (APCs) in the priming of NP-specific CTL in vivo. In this system, no evidence of direct CTL priming by tumor was detected. We have performed a similar analysis to determine if B7-1 transfectant of this tumor results in the direct priming of CTL, and to compare this response to that primed by host APCs. When H-2b-->H-2bxd bone marrow chimeras were immunized with a single injection of CT26/NP/B7-1 (H-2d), NP-specific CTL were detected that were restricted to the bone marrow haplotype (H-2b), but not to the tumor haplotype. In contrast, CTL recognizing the NP antigenic epitope in the context of the tumor's major histocompatibility complex were detectable only after multiple immunizations. These results suggest that whereas B7-1+ tumor vaccines result in some degree of direct presentation to CD8+ T cells, the dominant mechanism of CTL priming is through the uptake and presentation of tumor antigens by bone marrow-deprived APCs. However, repeated immunization with B7-1+ tumor cells can efficiently expand the directly primed CD8+ CTL population.

A reassessment of the role of B7-1 expression in tumor rejection.

Introduction of the B7-1 gene into murine tumor cells can result in rejection of the B7-1 transductants and, in some cases, systemic immunity to subsequent challenge with the nontransduced tumor cells. These effects have been largely attributed to the function of B7-1 as a costimulator in directly activating tumor specific, major histocompatibility class I-restricted CD8+ T cells. We examined the role of B7-1 expression in the direct rejection as well as in the induction of systemic immunity to a nonimmunogenic murine tumor. B-16 melanoma cells with high levels of B7-1 expression did not grow in C57BL/6 recipient mice, while wild-type B-16 cells and cells with low B7-1 expression grew progressively within 21 d. In mixing experiments with B7-1hi and wild-type B-16 cells, tumors grew out in vivo even when a minority of cells were B7-1-. Furthermore, the occasional tumors that grew out after injection of 100% B-16 B7-1hi cells showed markedly decreased B7-1 expression. In vivo antibody depletions showed that NK1.1 and CD8+ T cells, but not CD4+ T cells, were essential for the in vivo rejection of tumors. Animals that rejected B-16 B7-1hi tumors did not develop enhanced systemic immunity against challenge with wild-type B-16 cells. These results suggest that a major role of B7-1 expression by tumors is to mediate direct recognition and killing by natural killer cells. With an intrinsically nonimmunogenic tumor, this direct killing does not lead to enhanced systemic immunity.