A case of disseminated cryptococcosis with abdominal involvement due to Cryptococcus neoformans species complex in a Ragdoll cat and false-negative cryptococcal antigen lateral flow tests due to the postzone phenomenon.

Although cryptococcosis is the most common systemic fungal disease of cats, abdominal involvement is rarely reported. The pathogenesis of cryptococcosis usually involves sinonasal colonisation, followed by tissue invasion and sinonasal infection, with possible subsequent spread to the lungs and/or direct extension into the central nervous system (CNS), for example, via the cribriform plate. Further haematogenous spread can occur to any tissue, including skin and the CNS. This report describes a case of disseminated cryptococcosis due to Cryptococcus neoformans species complex in a 13-year-old cat, the fourth documented Australian feline case with abdominal involvement. The cat presented with a chronic history of upper respiratory disease that progressed to severe lethargy and anorexia. An autopsy revealed striking peritonitis with multifocal abdominal involvement affecting the liver, spleen, adrenal glands, kidneys, pancreas and mesentery. Cryptococcal organisms were also observed in organs within the thoracic cavity, sinonasal tissues and the CNS. Testing of abdominal fluid and serum for cryptococcal antigen using a commercially available lateral flow assay using neat fluid specimen initially tested false-negative. However, after dilution of the sample to 1:64, a positive result was obtained, confirming a postzone phenomenon. Taken together, the collective findings were indicative of widely disseminated cryptococcosis due to Cryptococcus neoformans with atypical involvement of the abdominal cavity.

Emerging leptospirosis in urban Sydney dogs: a case series (2017-2020).

Canine leptospirosis has not been reported in the Sydney dog population since 1976. However, between 2017 and 2020, leptospirosis was confirmed in 17 dogs, five of which were known to hunt rodents. Dogs infected between 2017 and 2019 lived within a 3 km radius in the Inner City of Sydney (n = 11). In 2020, cases emerged across a broader area of Sydney; Inner City (n = 1), Inner West (n = 3), Lower North Shore (n = 1) and Upper North Shore (n = 1). The disease was characterised by severe hepatorenal involvement resulting in an unusually high case fatality rate (88%). In conjunction with supportive clinical signs, diagnosis was confirmed by real-time PCR on whole blood (n = 1), kidney (n = 1), urine (n = 4), whole blood and urine (n = 9) or by seroconversion (n = 3). Antibody titres determined by Microscopic Agglutination Test (MAT) to Leptospira serovars were measured in 12 dogs: seven were positive for serovar Copenhageni, one was positive for serovar Hardjo, three were negative for all serovars, likely due to insufficient time for seroconversion before death and one had a low positive titre (1/50) for serovars Australis and Robinsoni. This sudden emergence of a highly fatal disease in pet dogs in Sydney has led to the introduction of Leptospira vaccination protocols for dogs living in inner Sydney using a monovalent vaccine containing serovar Copenhageni. The success of this vaccination program will require ongoing research to understand the emergence of leptospirosis in this region and the serovars involved.

Neural tube defects in four Shetland sheepdog puppies: clinical characterisation and computed tomography investigation.

BACKGROUND: Here, we report on the occurrence of neural tube defects (NTDs) in four related Shetland sheepdog puppies. NTDs present as a range of congenital malformations affecting the spine, skull and associated structures. Despite the severity of these malformations and their relatively high prevalence in humans, the aetiology is not well understood. It is even less well characterised in veterinary medicine. CASE REPORT: Affected puppies were investigated using computed tomography (CT) and then necropsy. CT identified a range of brain and spine abnormalities in the affected animals, including caudal anencephaly, encephalocele, spina bifida and malformed vertebrae. Other observed abnormalities in these puppies, including cranioschisis, atresia ani and hydrocephalus, may be secondary to, or associated with, the primary NTDs identified. CONCLUSION: This case report describes multiple related cases of NTDs in an Australian cohort of dogs. This study also highlights the potential of advanced imaging techniques in identifying congenital anomalies in stillborn and neonatal puppies. Further research is required to investigate the aetiology of NTDs in this group of affected Shetland sheepdogs.

Mammary neoplasia in common brushtail possums: case report and retrospective identification of additional cases.

BACKGROUND: Mammary neoplasia in possums have been sporadically reported in the literature. CASE REPORT: An adult common brushtail possum with severe dyspnoea warranting euthanasia was submitted for postmortem examination. Necropsy revealed a firm pale tan multilobulated mammary mass which contained pale tan tissue on section. Mammary carcinoma with metastases to the lungs, pleura, intercostal muscles and reproductive tract was diagnosed microscopically. Spontaneous neoplasms in possums are rarely reported. To provide a comprehensive insight into possum neoplasia, a retrospective evaluation of female reproductive disorders of growth in common brushtail possums from the Australian Registry of Wildlife Health (ARWH), Taronga Zoo, and University of Sydney, Veterinary Pathology Diagnostic Services (VPDS), was performed to identify additional cases. CONCLUSION: The present report describes the first published case report of mammary carcinoma in a common brushtail possum. This article should serve as a valuable reference for the types and relative frequencies of female reproductive disorders of growth that occur in possum species.

Morbidity associated with the immediate vertical rectus abdominus myocutaneous flap reconstruction after radical pelvic surgery.

AIM: Patients who undergo radical pelvic surgery often have problems with perineal wound healing and pelvic collections. While there is recognition of the perineal morbidity, there also remains uncertainty around the benefit of vertical rectus abdominus myocutaneous (VRAM) flaps due to the balance between primary healing and the complications associated with this form of reconstruction. This study aimed to evaluate factors associated with significant flap and donor site related complications following VRAM flap reconstruction for radical pelvic surgery. METHOD: A retrospective analysis of VRAM flap related complications was undertaken from prospectively maintained databases for all patients undergoing radical pelvic surgery (2001- 2017) in two cancer centres. RESULTS: In all, 154 patients were identified [median age 62 years (range 26-89 years), 80 (52%) men]. Thirty-three (21%) patients experienced significant donor or flap related complications. Major complications (Clavien-Dindo ≥ 3) related to the abdominal donor site occurred in nine (6%) patients, while those related to the flap or perineal site occurred in 28 (18%) patients. Only smoking (P = 0.003) and neoadjuvant radiotherapy (P = 0.047) were associated with the development of significant flap related complications on univariate analysis. Flap related complications resulted in a significantly longer hospital stay (P < 0.001). CONCLUSION: Careful patient selection is required to balance the risks vs the benefits of VRAM flap reconstruction. Immediate VRAM reconstruction in patients undergoing radical pelvic surgery can achieve early healing and stable perineal closure; it has a low but significant morbidity. Major flap related complications are significantly associated with smoking status and neoadjuvant radiotherapy and result in a prolonged length of hospital stay.

Hypoventilation, cardiac dysrhythmia, and cardiac arrest following acute Brunfelsia species (Yesterday, today, tomorrow) intoxication in a dog.

BACKGROUND: Intoxication following ingestion of the popular garden shrub 'Yesterday, today, tomorrow' (Brunfelsia sp.) is known to result in gastrointestinal and central nervous system clinical signs in dogs. CASE REPORT: A 2-year-old dog developed acute-onset vomiting, profuse diarrhoea and ptyalism after unsupervised access to an enclosed backyard that contained a Brunfelsia sp. shrub. During initial assessment the watery diarrhoea contained plant material and the dog appeared painful on abdominal palpation. Soon after admission, severe neurological abnormalities developed. Decontamination was undertaken by gastric and colonic lavage under general anaesthesia, but on recovery the patient had generalised seizures that were unresponsive to benzodiazepines. Following treatment with multiple antiepileptic medications and endotracheal intubation for loss of gag reflex, the patient developed respiratory failure requiring mechanical ventilation. Four days after initial presentation, the patient developed cardiac dysrhythmia leading to fatal cardiac arrest. Plant material recovered from the shrub and the patient's gastrointestinal tract were identified as Brunfelsia spp. CONCLUSION: This is the first report of hypoventilation, severe cardiac dysrhythmia and cardiac arrest associated with Brunfelsia sp. intoxication in a dog. Previous reports described clinical signs of gastrointestinal disease and mild cardiac dysrhythmia progressing to seizure activity and opisthotonus. Electrocardiography should form part of patient monitoring and mechanical ventilation considered for patients that develop respiratory failure, especially if massive ingestion is suspected.

Compensatory gastric stretching following subtotal gastric resection due to gastric adenocarcinoma in a diamond python (Morelia spilota spilota).

CASE REPORT: A 7-year-old male diamond python (Morelia spilota spilota) presented with a 2-month history of anorexia and a discrete intracoelomic mass, approximately 15 cm in length, located 90 cm from the head and approximately two-thirds of the snout to vent length. Physical examination determined the mass was likely to be stomach, testes or the right kidney. Radiographs showed a soft tissue opacity mass in the region of the stomach; fine needle aspirate demonstrated cellular debris admixed with bacteria and degenerate heterophils. Exploratory coeliotomy revealed a gastric mass involving 90% of the length of the stomach, partially occluding the gastric lumen. A subtotal gastrectomy was performed; the neoplastic tissue was removed with 2 cm margins, leaving 1 cm of stomach wall and the pyloric sphincter caudally that was anastomosed to the oesophagus. Four large nematodes were found within the necrotic lumen of the mass tightly adhered to the gastric mucosa. Ascarid nematodes were identified morphologically and further confirmed by molecular diagnostics as Ophidascaris spp. Histopathological evaluation of the excised mass revealed a gastric adenocarcinoma. Postoperatively the snake suffered from gastrointestinal dysfunction and maldigestion and was managed with slurry feeding for month. Three months postoperatively the snake was gaining weight, eating without assistance and digesting whole prey, which was incrementally increased in size. Gastroscopy 6 months postoperatively revealed the presence of a functional stomach with a functional pyloric sphincter and 8.5 cm of gastric mucosa caudal to the anastomosis between the oesophagus and stomach. CONCLUSION: This is the first report of almost complete subtotal gastric resection in an Australian python, with evidence of compensatory gastric stretching resulting in a functional stomach.

Surveillance imaging with FDG-PET/CT in the post-operative follow-up of stage 3 melanoma.

Background: As early detection of recurrent melanoma maximizes treatment options, patients usually undergo post-operative imaging surveillance, increasingly with FDG-PET/CT (PET). To assess this, we evaluated stage 3 melanoma patients who underwent prospectively applied and sub-stage-specific schedules of PET surveillance. Patients and methods: From 2009, patients with stage 3 melanoma routinely underwent PET +/- MRI brain scans via defined schedules based on sub-stage-specific relapse probabilities. Data were collected regarding patient characteristics and outcomes. Contingency analyses were carried out of imaging outcomes. Results: One hundred and seventy patients (stage 3A: 34; 3B: 93; 3C: 43) underwent radiological surveillance. Relapses were identified in 65 (38%) patients, of which 45 (69%) were asymptomatic. False-positive imaging findings occurred in 7%, and 6% had treatable second (non-melanoma) malignancies. Positive predictive values (PPV) of individual scans were 56%-83%. Negative scans had predictive values of 89%-96% for true non-recurrence [negative predictive values (NPV)] until the next scan. A negative PET at 18 months had NPVs of 80%-84% for true non-recurrence at any time in the 47-month (median) follow-up period. Sensitivity and specificity of the overall approach of sub-stage-specific PET surveillance were 70% and 87%, respectively. Of relapsed patients, 33 (52%) underwent potentially curative resection and 10 (16%) remained disease-free after 24 months (median). Conclusions: Application of sub-stage-specific PET in stage 3 melanoma enables asymptomatic detection of most recurrences, has high NPVs that may provide patient reassurance, and is associated with a high rate of detection of resectable and potentially curable disease at relapse.

Unusual presentation of neosporosis in a neonatal puppy from a litter of bulldogs.

CASE REPORT: A 17-day-old Bulldog puppy died soon after presentation for weakness and tachypnoea. Gross lesions included diffuse pulmonary oedema and a region of myocardial pallor that resembled an infarct. Inflammation was observed histopathologically in many organs, with numerous clusters of intracellular protozoa that stained positively using Neospora caninum immunohistochemistry. Myocarditis was severe and had associated necrosis of individual myocytes, but the tissue was not infarcted. The bitch had an antibody titre of 1 : 1600 for N. caninum. All six littermates were sold and reported to be healthy at 6 months of age. CONCLUSION: Unusual aspects of this case include the occurrence of clinical disease in only 1 of 7 neonatal puppies, widespread dissemination of the organism in multiple tissues, and regional pallor associated with myocarditis that gave a false gross appearance of infarction. This report also adds Bulldogs to the list of dog breeds shown to be susceptible to clinical neosporosis.

Localized melanoma in older patients, the impact of increasing age and comorbid medical conditions.

BACKGROUND: Elderly patients experience a different spectrum of disease and poorer outcomes than younger patients. This study investigated the impact of age and medical comorbidities on the management and outcome of patients ≥65 years. METHODS: A retrospective review of all patients ≥65 years (481 patients with 525 primary melanomas) presenting with AJCC clinical stage I-II melanoma to an Australian cancer centre between 2000 and 2008. RESULT: The median age was 74 years (65-94) with a male predominance (313 males, 65.0%) and median tumour thickness of 1.90 mm (IQR = 0.40-2.90, T1 = 33%, T2 = 20%, T3 = 24%, T4 = 23%). Inadequate surgical margins of excision (<10 mm) were common in older patients independent of site, thickness and ulceration (OR = 1.04, 95%CI = 1.00-1.07, p = 0.038). Inadequate excision margins were strongly associated with time to local recurrence, independent of age, thickness, ulceration and mitotic rate (HR = 3.00, 95%CI = 1.49-6.03, p = 0.0021), but not time to progression (p = 0.10) or disease specific survival (DSS, p = 0.27). Overall survival (OS) was strongly related to increasing age (HR = 1.04, 95%CI = 1.01-1.07, p = 0.015) and comorbid medical conditions (HR = 1.26, 95%CI = 1.12-1.42, p < 0.001), as assessed by the Charlson comorbidity index (CCI). DSS was significantly related to CCI (HR = 1.20, 95%CI = 1.01-1.42, p = 0.041) and not age (p = 0.46), when adjusting for thickness, ulceration and mitotic rate on multivariate analysis. CONCLUSION: Older patients present with poor prognosis melanomas yet are less likely to receive adequate surgical excision margins resulting in higher rates of local recurrence. In melanoma patients ≥65 years, the increasing number of medical comorbidities explains much of the age related variations in OS and DSS and should be considered when planning treatment.

Mortality in northern corroboree frog tadpoles (Pseudophryne pengilleyi) associated with Tetrahymena-like infection.

CASE REPORT: Mortality of northern corroboree frog tadpoles and eggs occurred in association with Tetrahymena-like ciliates. The predominant lesions in the tadpoles were inflammation and necrosis of the dermis and skeletal muscle. Some of the egg capsules also contained ciliates, but were overgrown with bacteria and fungi. CONCLUSION: Disease occurred, secondary to underlying husbandry issues, and resolved following their correction.

An effective AIDS vaccine based on live attenuated vesicular stomatitis virus recombinants.

We developed an AIDS vaccine based on attenuated VSV vectors expressing env and gag genes and tested it in rhesus monkeys. Boosting was accomplished using vectors with glycoproteins from different VSV serotypes. Animals were challenged with a pathogenic AIDS virus (SHIV89.6P). Control monkeys showed a severe loss of CD4+ T cells and high viral loads, and 7/8 progressed to AIDS with an average time of 148 days. All seven vaccinees were initially infected with SHIV89.6P but have remained healthy for up to 14 months after challenge with low or undetectable viral loads. Protection from AIDS was highly significant (p = 0.001). VSV vectors are promising candidates for human AIDS vaccine trials because they propagate to high titers and can be delivered without injection.

Direct measurement of CD4+ and CD8+ T-cell responses to CMV in HIV-1-infected subjects.

Data from murine models of chronic viral infection suggest that CD4+ T-cell responses to viral pathogens are important in sustaining the number and/or function of CD8+ cytotoxic T-cell (CTL) effectors. In this study, we used cytokine flow cytometry (CFC), staining with HLA-A*0201-peptide tetramers, and peptide stimulation with epitopic peptides to study functional CD4+ and CD8+ T-cell responses to cytomegalovirus (CMV) in human subjects coinfected with CMV and the human immunodeficiency virus, type 1 (HIV-1). We show that strong CD4+ and CD8+ T-cell responses to CMV antigens are sustained over time in HIV-1-infected individuals. Those who maintain a strong CD4+ T-cell response to CMV are also likely to maintain higher frequencies of CD8+ T cells capable of binding to HLA-A*0201-CMV pp65 (A2-pp65) tetramers as well as responses to pp65 peptide stimulation with effector cytokine production. These data support the hypothesis that declines in frequencies of CD4+ T-cell responses to CMV are associated with an inability to sustain high levels of CMV-specific CD8+ T-cell responses in HIV-1-infected subjects. These declines may precede the onset of CMV-associated end organ disease.

Requirement of mature dendritic cells for efficient activation of influenza A-specific memory CD8+ T cells.

It is critical to identify the developmental stage of dendritic cells (DCs) that is most efficient at inducing CD8+ T cell responses. Immature DCs can be generated from monocytes with GM-CSF and IL-4, while maturation is accomplished by the addition of stimuli such as monocyte-conditioned medium, CD40 ligand, and LPS. We evaluated the ability of human monocytes and immature and mature DCs to induce CD8+ effector responses to influenza virus Ags from resting memory cells. We studied replicating virus, nonreplicating virus, and the HLA-A*0201-restricted influenza matrix protein peptide. Sensitive and quantitative assays were used to measure influenza A-specific immune responses, including MHC class I tetramer binding assays, enzyme-linked immunospot assays for IFN-gamma production, and generation of cytotoxic T cells. Mature DCs were demonstrated to be superior to immature DC in eliciting IFN-gamma production from CD8+ effector cells. Furthermore, only mature DCs, not immature DCs, could expand and differentiate CTL precursors into cytotoxic effector cells over 7 days. An exception to this was immature DCs infected with live influenza virus, because of the virus's known maturation effect. Finally, mature DCs pulsed with matrix peptide induced CTLs from highly purified CD8+ T cells without requiring CD4+ T cell help. These differences between DC stages were independent of Ag concentrations or the number of immature DCs. In contrast to DCs, monocytes were markedly inferior or completely ineffective stimulators of T cell immunity. Our data with several qualitatively different assays of the memory CD8+ T cell response suggest that mature cells should be considered as immunotherapeutic adjuvants for Ag delivery.

HIV-specific CD8(+) T cells produce antiviral cytokines but are impaired in cytolytic function.

The use of peptide-human histocompatibility leukocyte antigen (HLA) class I tetrameric complexes to identify antigen-specific CD8(+) T cells has provided a major development in our understanding of their role in controlling viral infections. However, questions remain about the exact function of these cells, particularly in HIV infection. Virus-specific cytotoxic T lymphocytes exert much of their activity by secreting soluble factors such as cytokines and chemokines. We describe here a method that combines the use of tetramers and intracellular staining to examine the functional heterogeneity of antigen-specific CD8(+) T cells ex vivo. After stimulation by specific peptide antigen, secretion of interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, macrophage inflammatory protein (MIP)-1beta, and perforin is analyzed by FACS((R)) within the tetramer-positive population in peripheral blood. Using this method, we have assessed the functional phenotype of HIV-specific CD8(+) T cells compared with cytomegalovirus (CMV)-specific CD8(+) T cells in HIV chronic infection. We show that the majority of circulating CD8(+) T cells specific for CMV and HIV antigens are functionally active with regards to the secretion of antiviral cytokines in response to antigen, although a subset of tetramer-staining cells was identified that secretes IFN-gamma and MIP-1beta but not TNF-alpha. However, a striking finding is that HIV-specific CD8(+) T cells express significantly lower levels of perforin than CMV-specific CD8(+) T cells. This lack of perforin is linked with persistent CD27 expression on HIV-specific cells, suggesting impaired maturation, and specific lysis ex vivo is lower for HIV-specific compared with CMV-specific cells from the same donor. Thus, HIV-specific CD8(+) T cells are impaired in cytolytic activity.

Direct measurement of CD8+ T cell responses in macaques infected with simian immunodeficiency virus.

The simian immunodeficiency virus (SIV) macaque model system has been used extensively to study AIDS pathogenesis and to test candidate vaccines for their ability to protect against homologous or heterologous challenge with pathogenic SIV or SHIV. Recent studies suggest that stimulation of HIV-1-specific CTL responses is important for effective vaccination against HIV-1. While quantitative measurements of SIV-specific cytotoxic T lymphocyte (CTL) responses have been facilitated by the use of tetrameric peptide complexes, this technique is currently limited to the study of Mamu-A*01-positive rhesus macaques. Furthermore, very few SIV-specific CTL epitopes have been identified, and there is limited identification of other MHC alleles in macaques. In this study, cytokine flow cytometry (CFC) was used to quantify SIV-specific CD8+ antigen-reactive T cells in macaques infected with SIV. We found a strong correlation (r = 0.96, P < 0.001) between CD8+ antigen-reactive T cells stained with the Mamu-A*01 p11C, C-M tetramer and production of intracellular TNF-alpha in the CFC assay. Furthermore, the CFC assay was used to identify a novel SIV-specific CTL epitope in Envelope (SIV Env, a.a. 486-494, sequence AEVAELYRL). The use of the CFC assay facilitates the study of antigen-reactive T cell responses in SIV infection and vaccination.

Strong human immunodeficiency virus (HIV)-specific CD4+ T cell responses in a cohort of chronically infected patients are associated with interruptions in anti-HIV chemotherapy.

Virus-specific CD4+ T-helper cell function is important in controlling human immunodeficiency virus (HIV) infection but is impaired in patients with progressive HIV disease. It has been reported that after highly active antiretroviral therapy (HAART), HIV-specific lymphoproliferative responses remain absent, whereas responses to non-HIV microbial antigens are restored. However, in analyzing immune responses in a cohort of chronically infected adults on HAART, we observed strong HIV-specific CD4+ T cell responses of Th-1 phenotype in 11 of 22 patients. The magnitude and frequency of HIV-specific lymphoproliferative responses was strongly associated with previous interruptions in HAART (P=.001). In contrast, the magnitude of CD8+ T cell responses to HIV Gag, Pol, Env, and Nef was similar in patients who had and those who had not interrupted HAART. We conclude that (1) a significant proportion of chronically HIV-infected patients on HAART can generate strong HIV-specific CD4+ and CD8+ T cell immunity and (2) transient interruptions in antiviral treatment may prime or boost HIV-specific CD4+ T-helper responses.

Human immunodeficiency virus type 1- and cytomegalovirus-specific cytotoxic T lymphocytes can persist at high frequency for prolonged periods in the absence of circulating peripheral CD4(+) T cells.

CD4(+) T cells are thought to be critical in the maintenance of virus-specific CD8(+) cytotoxic T-cell (CTL) responses. In human immunodeficiency virus type 1 (HIV-1) infection, a selective decline in HIV-1-specific CTL as the CD4(+) T-cell count decreases has been reported. Using HLA-peptide tetrameric complexes, we show the presence at high frequency of HIV-1- and cytomegalovirus-specific CD8(+) T cells when the peripheral CD4(+) T-cell count was low or zero in three HIV-1-infected patients. No direct virus-specific CD8(+)-mediated effector activity was seen in these subjects, suggesting antigen unresponsiveness, although tetramer-sorted cells could be expanded in vitro in the presence of interleukin-2 into responsive effector cells. Thus, virus-specific CD8(+) T cells can be maintained in the peripheral circulation at high frequency in the absence of circulating peripheral CD4(+) T cells, but these cells may lack direct effector activity. Strategies designed to overcome this antigen unresponsiveness may be of value in therapies for the treatment of AIDS.

Simian immunodeficiency virus-specific cytotoxic T lymphocytes and protection against challenge in rhesus macaques immunized with a live attenuated simian immunodeficiency virus vaccine.

In this study, we examined the role of simian immunodeficiency virus (SIV)-specific cytotoxic T lymphocytes (CTLs) in macaques immunized with an attenuated strain of simian immunodeficiency virus (SIVmac239Deltanef) in protection against pathogenic challenge with SIVmac251. Our results indicate that attenuated SIVmac239Deltanef can elicit specific CTL precursor cells (CTLp), but no correlation was observed between breadth or strength of CTLp response to structural proteins SIV-Env, -Gamg or -Pol (as measured by limiting dilution assay) and protection against infection. In one animal, we longitudinally followed the SIV-Gag-specific response to an MHC class I Mamu-A*01-restricted epitope p11C, C-M using a tetrameric MHC/peptide complex reagent. A low frequency of SIV p11C, C-M peptide-specific tetramer-reactive cells was present at the time of challenge but could be expanded in vitro. Surprisingly, the low level of Mamu-A*01/p11C, C-M-specific CTLs induced through attenuated SIVmac239Deltanef vaccination increased in the absence of detectable SIVmac251 or SIVmac239Deltanef proviral DNA. Overall, our results suggest that protection against infection in this model can be achieved through more than one mechanism, with SIV-specific CTLs being important in controlling SIVmac239Deltanef viral replication postchallenge.