The Influence of Cytomegalovirus on Expression of HLA-G and its Ligand KIR2DL4 by Human Peripheral Blood Leucocyte Subsets.

HLA-G is a non-classical class I HLA antigen, normally expressed in high levels only on extravillous cytotrophoblast. It has immunosuppressive properties in pregnancy and has also been found to be upregulated on leucocytes in viral infection. In this study, proportions of all leucocyte subsets expressing HLA-G were found to be low in healthy subjects positive or negative for cytomegalovirus (CMV). Significantly greater proportions of CD4+ CD69+ and CD56+ T cells expressed HLA-G compared to other T cells. However, following stimulation with CMV antigens or intact CMV, proportions of CD4+, CD8+, CD69+ and CD56+ T cells, and also B cells expressing HLA-G, were significantly increased in CMV+ subjects. Despite some subjects having alleles of HLA-G associated with high levels of expression, no relationship was found between HLA-G genotype and expression levels. Purified B cells from CMV+ subjects stimulated in mixed culture with CMV antigens showed significantly increased HLA-G mRNA expression by real-time polymerase chain reaction. Serum levels of soluble HLA-G were similar in CMV- and CMV+ subjects but levels in culture supernatants were significantly higher in cells from CMV+ than from CMV- subjects stimulated with CMV antigens. The HLA-G ligand KIR2DL4 was mainly expressed on NK cells and CD56+ T cells with no differences between CMV+ and CMV- subjects. Following stimulation with IL-2, an increase in the proportion of CD56+ T cells positive for KIR2DL4 was found, together with a significant decrease in CD56dimCD16+ NK cells. The results show that CMV influences HLA-G expression in healthy subjects and may contribute to viral immune evasion.

CD56+ T cells are increased in kidney transplant patients following cytomegalovirus infection.

BACKGROUND: CD56+ T cells previously have been identified as potentially cytotoxic lymphocytes, and relative numbers are increased in some infectious diseases. PATIENTS AND METHODS: Relative proportions of CD56+ T cells were measured by flow cytometry in groups of renal transplant patients differing in cytomegalovirus (CMV) status of donor (D) and recipient (R). These measurements were related to episodes of CMV viremia. RESULTS: Patient groups in which recipients (R+) or donors (D+/R-) were CMV+ had significantly higher proportions of CD56+ T cells (5.11 ± 0.69% and 5.42 ± 1.01%, respectively) than the D-/R- group (1.9 ± 0.35%; P = 0.0018 and 0.017, respectively). In the high-risk D+/R- group, it was found that patients who had post-transplant CMV viremia had higher levels than those who remained CMV negative (9.09 ± 2.34% vs. 3.16 ± 1.22%; P = 0.01). CD56+ T cells from R+ and D+/R- groups had higher proportions of both CD4+ and CD8+ cells than the D-/R- group. When activation markers were examined, some CD56+ T cells from both CMV+ groups had a TEM phenotype, with significantly more expressing CD45RO and NKG2C, and less expressing CD28, CD62L, CD127, and CD161 compared to the D-/R- group. Some CD56+ T cells showed specificity for CMV antigens and similar proportions of CD8+ cells were positive for class I HLA-CMV tetramers containing immunodominant CMV peptides compared to the majority CD56- T cells. CONCLUSION: The results show significant increases in proportions of CD56+ T cells in relation to CMV infection in renal transplant patients and suggest that these cells have a cytotoxic function against CMV-infected cells.

Cytomegalovirus drives Vδ2neg γδ T cell inflation in many healthy virus carriers with increasing age.

Cytomegalovirus (CMV) usually causes lifelong asymptomatic infection, but over time can distort immune profiles. Recent reports describe selective expansion of Vδ2(neg) γδ T cells in healthy and immunocompromised CMV carriers. Having shown previously that virus-specific CD8(+) and CD4(+) T cell responses are increased significantly in elderly CMV carriers, probably driven by chronic stimulation, we hypothesized that Vδ2(neg) γδ T cells may also be expanded with age. Our results show that Vδ2(neg) γδ T cells are increased significantly in CMV-seropositive healthy individuals compared to CMV-seronegative controls in all age groups. The differences were most significant in older age groups (P < 0·0001). Furthermore, while Vδ2(neg) γδ T- cells comprise both naive and memory cells in CMV-seronegative donors, highly differentiated effector memory cells are the dominant phenotype in CMV carriers, with naive cells reduced significantly in numbers in CMV-seropositive elderly. Although phenotypically resembling conventional CMV-specific T cells, Vδ2(neg) γδ T cells do not correlate with changes in magnitude of CMV-specific CD4(+) or CD8(+) T cell frequencies within those individuals, and do not possess ex-vivo immediate effector function as shown by CMV-specific CD4(+) and CD8(+) T cells. However, after short-term culture, Vδ2(neg) γδ T cells demonstrate effector T cell functions, suggesting additional requirements for activation. In summary, Vδ2(neg) γδ T cells are expanded in many older CMV carriers, demonstrating a further level of lymphocyte subset skewing by CMV in healthy individuals. As others have reported shared reactivity of Vδ2(neg) γδ T cells towards tumour cells, the composition of γδ T cell subsets may also have implications for risk of developing cancer in elderly people.

Hydroxychloroquine therapy in patients with primary Sjögren's syndrome may improve salivary gland hypofunction by inhibition of glandular cholinesterase.

OBJECTIVE: To determine whether (i) cholinesterase activity is increased in the saliva of patients with primary Sjogren's syndrome (pSS), (ii) increased levels of cholinesterase of lymphocyte origin could interfere with the secretory activity of submandibular acinar cells, and (iii) hydroxychloroquine at therapeutic doses could interfere with cholinesterase activity. METHODS: The Ellman method was used to determine the levels of salivary cholinesterase activity and the K(i) of both chloroquine and hydroxychloroquine for serum cholinesterase. The ability of lymphocyte cholinesterase to inhibit the acetylcholine (ACh)-evoked rise in [Ca(2+)](i) in mouse submandibular acinar cells was determined using fura-2 microfluorimetry. RESULTS: Patients with pSS had significantly higher levels of cholinesterase activity in both their unstimulated (P < 0.05) and stimulated saliva (P < 0.0001) compared with control subjects. Lymphocyte cholinesterase was capable of inhibiting the ACh-evoked rise in [Ca(2+)](i). The in vitro K(i) for hydroxychloroquine inhibition of cholinesterase was 0.38 +/- 1.4 microM. CONCLUSION: These data suggest that increased levels of cholinesterase present in the salivary glands of patients with pSS may contribute to glandular hypofunction and provide evidence that the therapeutic enhancement of salivary secretion in patients with pSS by hydroxychloroquine may be mediated by inhibition of glandular cholinesterase activity, although further in vivo investigation is needed.

Treatment with Met-RANTES reduces lung injury in caerulein-induced pancreatitis.

BACKGROUND: Severe acute pancreatitis leads to a systemic inflammatory response characterized by widespread leucocyte activation and, as a consequence, distant lung injury. In CC chemokines the first two cysteine residues are adjacent to each other. The aim of this study was to evaluate the effect of Met-RANTES, a CC chemokine receptor antagonist, on pancreatic inflammation and lung injury in caerulein-induced acute pancreatitis in mice. METHODS: Acute pancreatitis was induced in mice by hourly intraperitoneal injection of caerulein. Met-RANTES was administered either 30 min before or 1 h after starting caerulein injections, and pancreatic inflammation and lung injury were assessed. There were five groups of eight mice each including controls. RESULTS: Treatment with Met-RANTES had little effect on caerulein-induced pancreatic damage. Met-RANTES, however, reduced lung injury when given either before administration of caerulein (mean(s.e.m.) lung myeloperoxidase (MPO) 1.47(0.19) versus 3.70(0.86)-fold increase over control, P = 0.024; mean(s.e.m.) microvascular permeability 1.15(0.05) versus 3.57(0.63) lavage to plasma fluorescein isothiocyanate-labelled albumin fluorescence ratio (L/P) per cent, P = 0.002) or after caerulein administration (lung MPO 1.96(0.27) versus 3.65(0.63)-fold increase over control, P = 0.029; microvascular permeability 0.94(0.04) versus 2.85(0.34) L/P per cent, P < 0.001). CONCLUSION: Treatment with Met-RANTES reduces lung damage associated with caerulein-induced pancreatitis in mice. Chemokine receptor antagonists may be of use for the treatment of the systemic complications of acute pancreatitis.

Natural killer cells in the synovial fluid of rheumatoid arthritis patients exhibit a CD56bright,CD94bright,CD158negative phenotype.

BACKGROUND: Natural killer (NK) cells play an important role in several animal models of autoimmunity by modulating T-cell responses, but it is unclear whether human NK cells have similar functions. METHODS: We characterized the phenotype of NK cells in synovial fluid (SF) and peripheral blood (PB) of patients with rheumatoid arthritis (RA) and in healthy control subjects using flow cytometry and quantitative PCR. RESULTS: The proportions of NK cells in PB and SF of RA patients were not significantly different from those in healthy PB. However, the SF NK cell phenotype was strikingly different, with increased CD94 and CD56 densities and greatly reduced proportions of cells expressing CD158a/b. These cells also had reduced mRNAs coding for CD158a/b and low perforin levels compared with RA PB and healthy PB NK cells. CONCLUSIONS: We identified a novel phenotype of SF NK cells that is of potential significance in RA. Experiments are now under way to determine the function of these SF NK cells and their potential role in RA.

Levels of the chemokines growth-related oncogene alpha and epithelial neutrophil-activating protein 78 are raised in patients with severe acute pancreatitis.

BACKGROUND: Multiple organ dysfunction syndrome secondary to systemic leucocyte activation is the major cause of death following an attack of acute pancreatitis. Although plasma levels of interleukin (IL) 8 are known to be raised in acute pancreatitis, levels of other CXC chemokines such as growth-related oncogene (GRO) alpha and epithelial neutrophil-activating protein (ENA) 78, which are also potent neutrophil chemoattractants and activators, have not been measured. METHODS: Timed plasma samples were obtained from 51 patients with acute pancreatitis, 27 with a severe attack and 24 with mild disease according to the Atlanta classification. Samples were analysed to determine levels of C-reactive protein (CRP), IL-8, GRO-alpha and ENA-78. RESULTS: Plasma levels of IL-8, GRO-alpha and ENA-78 were increased in patients with severe as opposed to mild acute pancreatitis as early as 24 h following disease onset. Using cut-off levels of 7 pg/ml for IL-8, 70 pg/ml for GRO-alpha and 930 pg/ml for ENA-78, peak levels within the first 24 h of admission had an accuracy of 81, 71 and 87 per cent respectively in predicting the severity of an attack of acute pancreatitis. CONCLUSION: In patients with severe acute pancreatitis plasma levels of GRO-alpha and ENA-78 were raised in addition to those of IL-8, suggesting that all three chemokines are involved in the inflammatory response in this condition.

Direct evidence that leukemic cells present HLA-associated immunogenic peptides derived from the BCR-ABL b3a2 fusion protein.

The BCR-ABL oncogene is central in the pathogenesis of chronic myeloid leukemia (CML). Here, tandem nanospray mass spectrometry was used to demonstrate cell surface HLA-associated expression of the BCR-ABL peptide KQSSKALQR on class I-negative CML cells transfected with HLA-A*0301, and on primary CML cells from HLA-A3-positive patients. These patients mounted a cytotoxic T-lymphocyte response to KQSSKALQR that also killed autologous CML cells, and tetramer staining demonstrated the presence of circulating KQSSKALQR-specific T cells. The findings are the first demonstration that CML cells express HLA-associated leukemia-specific immunogenic peptides and provide a sound basis for immunization studies against BCR-ABL.

BCR-ABL fusion peptides and cytotoxic T cells in chronic myeloid leukaemia.

The BCR-ABL gene that arises in chronic myeloid leukaemia (CML) is a neoantigen. Peptides derived from the BCR-ABL fusion junction may therefore be immunogenic, if appropriately presented to the immune system. This article reviews data demonstrating that certain junctional peptides will bind to HLA molecules, and that these peptides will elicit specific T-lymphocyte responses in vitro, in both normal subjects and in CML patients. The clinical relevance of these observations is discussed.

Peritoneal fluid concentrations of interleukin-4 in relation to the presence of endometriosis, its stage and the phase of the menstrual cycle.

BACKGROUND: Interleukin-4 (IL-4) is a cytokine with both stimulatory and inhibitory effects on the inflammatory system such as macrophage inhibition and T-cell activation. It is known to regulate several monocyte functions, including inhibition of the synthesis of cytokines such as IL-1, IL-6 and TNF-alpha as well as potentiating IL-8. METHOD: In an attempt to clarify the association between IL-4 and endometriosis, we measured the concentration of IL-4 in the peritoneal fluid of 52 women; 24 with endometriosis and 28 with no endometriosis, controlling for the phase of the cycle and the stage of disease. RESULTS: There was no difference in the concentrations of IL-4 between women with (n=28) and without endometriosis (n=24). No difference was found between the IL-4 concentrations in women with different stages of endometriosis. Levels of IL-4 did not show a difference according to the phase of the cycle in either group. CONCLUSION: Our results indicate no association between peritoneal fluid levels of IL-4 and endometriosis and hence suggest that IL-4 is not involved in the pathogenesis of endometriosis.

Concentration of interleukin-12 in the peritoneal fluid is not influenced by the presence of endometriosis, its stage or the phase of the menstrual cycle.

BACKGROUND: IL-12 is a key immunomodulatory cytokine. Its presence or concentration in peritoneal fluid is not related to the presence of endometriosis or the stage of the disease. A study was carried out to gain insight into the role of IL-12 in the development and maintenance of endometriosis in relation to menstrual cycle. METHODS: A prospective study recruiting 64 consecutive women undergoing laparoscopic surgery for benign gynecological indications. Peritoneal fluid was obtained during laparoscopy. Concentration of IL-12 was measured and correlated to the presence of endometriosis, its stage and the phase of the menstrual cycle. RESULT(S): Peritoneal fluid concentrations of IL-12 showed no correlation with the presence of endometriosis, the AFS stage of the disease or the phase of the menstrual cycle. CONCLUSION(S): IL-12 is a normal constituent of peritoneal fluid in around one third of the population tested and is not involved in the pathogenesis of endometriosis at any stage of the disease or the phase of the menstrual cycle.

Peritoneal fluid concentrations of interleukin-11 in women with endometriosis.

OBJECTIVE: To determine the peritoneal fluid concentrations of interleukin-11 (IL-11) in women with endometriosis as compared with the control group. DESIGN: A prospective, controlled study. SETTING: The obstetrics and gynecology department of a teaching hospital and a university immunology department. PATIENT(S): Sixty consecutive women undergoing laparoscopic surgery for benign gynecological indications. INTERVENTION(S): Peritoneal fluid was obtained during laparoscopy, and the concentration of IL-11 was measured. MAIN OUTCOME MEASURE(S): Concentration of IL-11 in correlation with the presence of endometriosis, its stage, and the phase of the menstrual cycle. RESULT(S): IL-11 was detectable in the peritoneal fluid of 64% of women tested. Concentrations of IL-11 showed no correlation with the presence of endometriosis, the American Fertility Society stage of the disease, or the phase of the menstrual cycle. CONCLUSION(S): We found no evidence to suggest that IL-11 is involved in the pathogenesis of pelvic endometriosis.

Treatment with neutralising antibody against cytokine induced neutrophil chemoattractant (CINC) protects rats against acute pancreatitis associated lung injury.

BACKGROUND: Lung injury manifest clinically as adult respiratory distress syndrome (ARDS) is a common cause of morbidity and mortality following acute pancreatitis (AP). Neutrophils play a critical role in the progression of AP to ARDS. C-x-C chemokines are potent neutrophil chemoattractants and activators and have been implicated in AP. AIMS: To evaluate the effect of blocking the C-x-C chemokine, cytokine induced neutrophil chemoattractant (CINC), in AP on pancreatic inflammation and the associated lung injury in rats. METHODS: AP was induced by hourly intraperitoneal injections of caerulein. Goat anti-CINC antibody was administered either before or after starting caerulein injections to evaluate the prophylactic and therapeutic effects, respectively. Severity of AP was determined by measuring plasma amylase, pancreatic water content, and pancreatic myeloperoxidase (MPO) activity as a measure of neutrophil sequestration in the pancreas. Lung injury was determined by measurement of pulmonary microvascular permeability and lung MPO activity. RESULTS: Treatment with anti-CINC antibody had little effect on caerulein induced pancreatic damage. However, it reduced the caerulein mediated increase in lung MPO activity as well as lung microvascular permeability when administered either prophylactically (lung MPO (fold increase over control): 1.53 (0.21) v. 3.30 (0.46), p<0.05; microvascular permeability (L/P%): 0.42 (0.07) v. 0.77 (0.11), p<0.05) or therapeutically (lung MPO (fold increase over control): 2.13 (0.10) v 4.42 (0.65), p<0.05; microvascular permeability (L/P%): 0.31 (0.05) v 0.79 (0.13), p<0.05). CONCLUSION: Treatment with anti-CINC antibody afforded significant protection against pancreatitis associated lung injury. These results suggest that CINC plays an important role in the systemic inflammatory response in AP.

Follicular fluid concentrations of interleukin-12 and interleukin-8 in IVF cycles.

OBJECTIVE: To investigate the role of interleukin-12 (IL-12) and IL-8 in the periovulatory follicular fluid during in vitro fertilization cycles. DESIGN: A prospective study. SETTING: Reproductive Medicine Unit, Liverpool Women's Hospital, United Kingdom. PATIENT(S): Women undergoing in vitro fertilization treatment. INTERVENTION(S): IL-8 and IL-12 concentrations in follicular fluid samples that had been collected during transvaginal oocyte retrieval were measured using an enzyme-linked immunosorbent assay (ELISA). Cytokine concentrations were correlated to fertilization rates and treatment outcome. MAIN OUTCOME MEASURE(S): Fertilization rates and ultrasonographic evidence of intrauterine pregnancy by 4 weeks after embryo transfer. RESULT(S): Failed fertilization in women with detectable IL-12 was significantly higher (45.5%) than in the IL-12 negative group (6.1%), P=.01. None of the women with detectable IL-12 achieved a pregnancy at the end of the treatment (P=.01). IL-8 was present in the follicular fluid of all women, and no difference in its concentrations was found between the pregnant and nonpregnant groups. No correlation was found between the follicular fluid concentrations of IL-8 and fertilization rates. CONCLUSION(S): The presence of IL-12 in the follicular fluid appears to be associated with a negative outcome in IVF treatment. Interleukin-8 appears to be an essential part of folliculogenesis, although its concentration is not associated with fertilization or implantation rates.

An investigation of interactions between the immune system and stimulus-secretion coupling in mouse submandibular acinar cells. A possible mechanism to account for reduced salivary flow rates associated with the onset of Sjögren's syndrome.

OBJECTIVES: To determine whether chronic exposure to lymphocyte-derived cytokines could inhibit the fluid secretory mechanism in salivary gland acinar cells and so account for the loss of gland function seen in the early stages of Sjögren's syndrome. METHODS: Mouse submandibular acinar cells maintained in primary culture were exposed to a profile of cytokines produced by concanavalin A-activated splenic lymphocytes in vitro for periods up to 72 h. Agonist-evoked changes in intracellular Ca(2+) were determined microfluorimetrically in both control and cytokine-treated cells. RESULTS: Acinar cells maintained in primary culture in the presence of cytokines for up to 72 h were able to mobilize intracellular calcium in response to stimulus by acetylcholine in an identical fashion to those maintained in primary culture in the absence of cytokines. Acute application of the conditioned medium produced by the activated lymphocytes had an antisecretory effect on acetylcholine-evoked Ca(2+) mobilization, which was found to be mediated by cholinesterase rather than by cytokines. CONCLUSION: Neither chronic nor acute exposure to the profile of cytokines released by concanavalin A-activated splenic lymphocytes interfered in any way with the second messenger cascade and fluid and electrolyte secretion in acinar cells. Our data suggest an alternative hypothesis, in which elevated levels of cholinesterase can metabolize acetylcholine released within the salivary glands and thus prevent fluid secretion.

b3a2 BCR-ABL fusion peptides as targets for cytotoxic T cells in chronic myeloid leukaemia.

Peptide sequences spanning the BCR-ABL protein junction potentially constitute novel leukaemia-specific antigens. 9-mer b3a2 fusion peptides have been reported to bind with high affinity to HLA-A3, -A11 and -B8. We have studied the effect of b3a2 BCR-ABL junctional peptides on the cytotoxic T-cell (CTL) response against normal and chronic myeloid leukaemia (CML) cells. Antigen-presenting cells (APCs) were prepared from HLA-A3- or -B8-positive peripheral blood mononuclear cells (PBMCs) by incubation with phytohaemagglutinin (PHA) and interleukin (IL)-2 for 7 d. These APCs were pulsed with the respective b3a2 junctional peptide in the presence of beta2-microglobulin and were then used to challenge autologous PBMCs at 7-d intervals in the presence of IL-2, IL-6, IL-7 and IL-12. On subsequent exposure to target cells (either further pulsed normal APCs or unpulsed CML cells), specific HLA-restricted CTL responses were observed against all HLA-A3/-B8 matched normal target cells tested, but not to targets that were HLA mismatched. Cytotoxicity was also induced against HLA-A3/-B8 unpulsed CML cells, but not against unmatched CML cells. These data indicate (i) that endogenous BCR-ABL junctional peptides may be presented by CML cells and (ii) that exogenous peptides are potential stimulators of autologous antileukaemic CTLs.

Inflammatory mediators in acute pancreatitis.

Inflammatory mediators play a key role in acute pancreatitis and the resultant multiple organ dysfunction syndrome, which is the primary cause of death in this condition. Recent studies have confirmed the critical role played by inflammatory mediators such as TNF-alpha, IL-1beta, IL-6, IL-8, PAF, IL-10, C5a, ICAM-1, and substance P. The systemic effects of acute pancreatitis have many similarities to those of other conditions such as septicaemia, severe burns, and trauma. The delay between the onset of inflammation in the pancreas and the development of the systemic response makes acute pancreatitis an ideal experimental and clinical model with which to study the role of inflammatory mediators and to test novel therapies. Elucidation of the key mediators involved in the pathogenesis of acute pancreatitis will facilitate the development of clinically effective anti-inflammatory therapy.

Interleukin-8 as an autocrine growth factor for human colon carcinoma cells in vitro.

Cell lines derived from human colon carcinomas secrete interleukin 8 (IL-8) in vitro and this chemokine has also been detected immunohistochemically in human colon carcinoma specimens, in which it is tumour cell associated. In these experiments, IL-8 was shown to comprise an important component of the angiogenic activity of colon carcinoma cell line supernatants. The effect of modulating IL-8 activity upon the growth of the colon carcinoma cell lines HCT116A, HT29 and CaCo2 was investigated. Supplementing endogenously produced IL-8 by recombinant chemokine led to stimulation of cell growth. Neutralization of the effect of endogenously produced IL-8, either with the specific antagonist peptide AcRRWWCR or with blocking anti-IL-8 antibody, resulted in around 50% inhibition of cell growth (P<0.05). All of the colon carcinoma cell lines tested expressed mRNA for both IL-8RA and RB when grown at confluence. At the protein level, all cell lines expressed IL-8RA. Expression of IL-8RB was weak, although increased expression was seen in HCT116A cells as they approached confluence. Antibodies to IL-8RA and RB did not affect proliferation at low cell density but were strongly inhibitory when cells were cultured at a higher density. These data suggest that IL-8 acts as an autocrine growth factor for colon carcinoma cell lines and would support the concept that a similar autocrine loop operates in vivo.

Combined suicide and granulocyte-macrophage colony-stimulating factor gene therapy induces complete tumor regression and generates antitumor immunity.

The use of prodrug-activated ("suicide") gene therapy has been shown to be effective in inducing tumor regression when only a small proportion of tumor cells contains the suicide gene. These experiments were designed to test whether additional therapeutic benefit may be obtained by stimulating the immune response. Murine MC26 colon carcinoma cells, either untransduced or transduced with genes for herpes simplex virus-1 thymidine kinase (HSV1-TK) or human GM-CSF, were injected subcutaneously into syngeneic BALB/c mice in various combinations. Inoculation of equal numbers of untransduced and HSV1-TK-containing cells followed by ganciclovir (GCV) treatment resulted in almost complete tumor regression, but by 7 weeks, tumors had recurred in all mice. A similar initial regression was obtained using equal numbers of cells containing HSV1-TK and GM-CSF genes, but >80% of these mice remained tumor-free after 3 months. Groups of tumor-free mice that had received GM-CSF-containing cells were left for different periods of time and rechallenged with unmodified MC26 cells on the opposite flank. Of the mice rechallenged 14, 28, and 108 days later, 100%, 88%, and 57%, respectively, showed complete resistance to unmodified tumor cells. In mice that showed tumor regrowth, tumor volume was much less than in control mice. Adoptive transfer of spleen cells from resistant mice to naïve syngeneic mice resulted in partial resistance to challenge with unmodified tumor cells. Specific cytotoxicity against MC26 cells was only demonstrable in mice receiving GM-CSF- and HSV1-TK-containing tumor cells. These experiments show that the presence of cells secreting GM-CSF in HSV1-TK-containing, regressing tumor is able to induce complete or partial resistance to tumor rechallenge. This indicates the potential usefulness of GM-CSF in enhancing other antitumor therapies.