Mucosal immunity and HIV-1 infection: applications for mucosal AIDS vaccine development

Medical Care for Tuberculosis-HIV-Coinfected Patients in Russia with Respect to a Changeable Patients’ Structure

To date, tuberculosis (TB) remains the primary cause of mortality in human immunodeficiency virus (HIV) patients in Russia. Since the beginning of 2000, a sharp change in the HIV patients’ structure, to the main known risk factors for HIV infection has taken place in Russia. The transmission of HIV through injectable drug use has begun to decline significantly, giving way to the prevalence of sexual HIV transmission today. These changes may require adjustments to organizational approaches to anti-TB care and the treatment of HIV-positive patients. Our study is aimed at identifying changes in TB-HIV coinfection patients’ structures in 2019 compared to 2000. Based on the results obtained, our goal was to point out the parameters that need to be taken into account when developing approaches to improve the organization of TB control care for people with HIV infection. We have carried out a cross-sectional, retrospective, epidemiological study using government TB registry data from four regions in two federal districts of Russia in 2019. The case histories of 2265 patients from two regions with high HIV prevalence, which are part of the Siberian Federal District of Russia, and 89 patient histories from two regions of low HIV prevalence, which are part of the Central Federal District of Russia, were analyzed. We found that parenteral transmission (69.4%) remains the primary route of HIV transmission among the TB-HIV coinfected. The unemployed of working age without disability account for 80.2% of all coinfected people, while the formerly incarcerated account for 53.7% and the homeless account for 4.1%. Those with primary multidrug-resistant TB (MDR-TB) comprise 56.2% of HIV-TB patients. When comparing the incidence of coinfection with HIV among TB patients, statistically significant differences were obtained. Thus, the chances of coinfection increased by 4.33 times among people with active TB (95% CI: 2.31; 8.12), by 2.97 times among people with MDR-TB (95% CI: 1.66; 5.32), by 5.2 times in people with advanced processes in the lungs, including destruction, (95% CI: 2.78; 9.7), as well as by 10.3 times in the case of death within the first year after the TB diagnosis (95% CI: 2.99; 35.5). The absence of data for the presence of TB during preventive examination was accompanied by a decrease in the chances of detecting coinfection (OR 0.36; 95% CI: 0.2; 0.64). We have identified the probable causes of the high incidence of TB among HIV-infected: HIV-patient social maladaptation usually results in delayed medical care, leading to TB treatment regimen violations. Furthermore, self-administration of drugs triggers MDR-TB within this group. Healthcare providers should clearly explain to patients the critical importance of immediately seeking medical care when initial TB symptoms appear.

Mycobacterium tuberculosis-Induced Bronchoalveolar Lavage Gene Expression Signature in Latent Tuberculosis Infection Is Dominated by Pleiotropic Effects of CD4+ T Cell-Dependent IFN-γ Production despite the Presence of Polyfunctional T Cells within the Airways

Tuberculosis (TB) remains a worldwide public health threat. Development of a more effective vaccination strategy to prevent pulmonary TB, the most common and contagious form of the disease, is a research priority for international TB control. A key to reaching this goal is improved understanding of the mechanisms of local immunity to Mycobacterium tuberculosis, the causative organism of TB. In this study, we evaluated global M. tuberculosis-induced gene expression in airway immune cells obtained by bronchoalveolar lavage (BAL) of individuals with latent TB infection (LTBI) and M. tuberculosis-naive controls. In prior studies, we demonstrated that BAL cells from LTBI individuals display substantial enrichment for M. tuberculosis-responsive CD4⁺ T cells compared with matched peripheral blood samples. We therefore specifically assessed the impact of the depletion of CD4⁺ and CD8⁺ T cells on M. tuberculosis-induced BAL cell gene expression in LTBI. Our studies identified 12 canonical pathways and a 47-gene signature that was both sensitive and specific for the contribution of CD4⁺ T cells to local recall responses to M. tuberculosis In contrast, depletion of CD8⁺ cells did not identify any genes that fit our strict criteria for inclusion in this signature. Although BAL CD4⁺ T cells in LTBI displayed polyfunctionality, the observed gene signature predominantly reflected the impact of IFN-γ production on a wide range of host immune responses. These findings provide a standard for comparison of the efficacy of standard bacillus Calmette-Guérin vaccination as well as novel TB vaccines now in development at impacting the initial response to re-exposure to M. tuberculosis in the human lung.

Mucosal Vaccine Approaches for Prevention of HIV and SIV Transmission

Optimal protective immunity to HIV will likely require that plasma cells, memory B cells and memory T cells be stationed in mucosal tissues at portals of viral entry. Mucosal vaccine administration is more effective than parenteral vaccine delivery for this purpose. The challenge has been to achieve efficient vaccine uptake at mucosal surfaces, and to identify safe and effective adjuvants, especially for mucosally administered HIV envelope protein immunogens. Here, we discuss strategies used to deliver potential HIV vaccine candidates in the intestine, respiratory tract, and male and female genital tract of humans and nonhuman primates. We also review mucosal adjuvants, including Toll-like receptor agonists, which may adjuvant both mucosal humoral and cellular immune responses to HIV protein immunogens.

Toward DNA-Based T-Cell Mediated Vaccines to Target HIV-1 and Hepatitis C Virus: Approaches to Elicit Localized Immunity for Protection

Human immunodeficiency virus (HIV)-1 and hepatitis C virus (HCV) are major contributors to the global disease burden with many experts recognizing the requirement of an effective vaccine to bring a durable end to these viral epidemics. The most promising vaccine candidates that have advanced into pre-clinical models and the clinic to eliminate or provide protection against these chronic viruses are viral vectors [e.g., recombinant cytomegalovirus, Adenovirus, and modified vaccinia Ankara (MVA)]. This raises the question, is there a need to develop DNA vaccines against HIV-1 and HCV? Since the initial study from Wolff and colleagues which showed that DNA represents a vector that can be used to express transgenes durably in vivo, DNA has been regularly evaluated as a vaccine vector albeit with limited success in large animal models and humans. However, several recent studies in Phase I-IIb trials showed that vaccination of patients with recombinant DNA represents a feasible therapeutic intervention to even cure cervical cancer, highlighting the potential of using DNA for human vaccinations. In this review, we will discuss the limitations and the strategies of using DNA as a vector to develop prophylactic T cell-mediated vaccines against HIV-1 and HCV. In particular, we focus on potential strategies exploiting DNA vectors to elicit protective localized CD8⁺ T cell immunity in the liver for HCV and in the cervicovaginal mucosa for HIV-1 as localized immunity will be an important, if not critical component, of an efficacious vaccine against these viral infections.

Live attenuated Salmonella displaying HIV-1 10E8 epitope on fimbriae: systemic and mucosal immune responses in BALB/c mice by mucosal administration

The HIV-1 membrane proximal external region (MPER) that is targeted by several broadly neutralizing antibodies (BNAbs) has been considered a potential immunogen for vaccine development. However, to date the immunogenicity of these BNAb epitopes has not been made sufficiently adequate. In the present work, we used live attenuated Salmonella as a platform to present the HIV-1 MPER 10E8 epitope in the fimbriae. The insertion of the 10E8 epitope into the fimbriae had no significant influence on the expression and the absorption capacity of bacterial fimbriae, nor on the virulence and invasiveness of the attenuated Salmonella. After oral administration of the vaccine construct to mice followed by 10E8 epitope peptide boost, specific antibody responses in serum and mucosa as well as memory lymphocytes in spleen and plasma cells in bone marrow were induced. We also found that the live attenuated Salmonella vector directed the immunity toward Th1 bias, induced Th1 and Th2 cytokine responses and stimulated significant B cell differentiation into GC B, memory B and plasma cells. Therefore, we propose that the live attenuated Salmonella constitutively expressing HIV-1 BNAb epitopes on the fimbriae will be an effective approach to improving immune microenvironment and enhancing the immunogenicity of HIV-1 epitope vaccines.

Intranasal Vaccination Affords Localization and Persistence of Antigen-Specific CD8⁺ T Lymphocytes in the Female Reproductive Tract

Immunization strategies generating large numbers of antigen-specific T cells in the female reproductive tract (FRT) can provide barrier protection against sexually-transmitted pathogens, such as the human immunodeficiency virus (HIV) and human papillomaviruses (HPV). The kinetics and mechanisms of regulation of vaccine-induced adaptive T cell-mediated immune responses in FRT are less well defined. We present here evidence for intranasal delivery of the model antigen ovalbumin (OVA) along with alpha-galactosylceramide adjuvant as a protein vaccine to induce significantly higher levels of antigen-specific effector and memory CD8⁺ T cells in the FRT, relative to other systemic and mucosal tissues. Antibody blocking of the CXCR3 receptor significantly reduced antigen-specific CD8⁺ T cells subsequent to intranasal delivery of the protein vaccine suggesting an important role for the CXCR3 chemokine-receptor signaling for T cell trafficking. Further, intranasal vaccination with an adenoviral vector expressing OVA or HIV-1 envelope was as effective as intramuscular vaccination for generating OVA- or ENV-specific immunity in the FRT. These results support the application of the needle-free intranasal route as a practical approach to delivering protein as well as DNA/virus vector-based vaccines for efficient induction of effector and memory T cell immunity in the FRT.

Intranasal Vaccination against HIV-1 with Adenoviral Vector-Based Nanocomplex Using Synthetic TLR-4 Agonist Peptide as Adjuvant

Recombinant type 5 adenovirus (rAd5) vaccines hold the promise to prevent HIV-1 infections. Intranasal vaccination not only stimulates systemic immunity but also elicits mucosal immunity that provides first defense for mucosally transmitted diseases like HIV-1. Adjuvants such as TLR agonists are usually codelivered with antigens to enhance the immunogenicity of vaccines. Here, we present a rAd5 vaccine delivery system using DEG-PEI as the carrier. Adenovirus encoding HIV gag was used as antigen, and was complexed with DEG-PEI polymer via electrostatic interaction. A novel synthetic TLR-4 agonist, RS09, was either chemically linked with DEG-PEI (DP-RS09) or physically mixed with it(DP/RS09) to enhance the immunogenticity of rAd5 vaccine. After intranasal immunization, the systemic antigen-specific immune responses and cytotoxicity T lymphocytes responses induced by DP-RS09-rAd5 and DP/RS09-rAd5 were analyzed. The mucosal secretory IgA level was detected in both nasal and vaginal washes to determine the mucosal immunity. Furthermore, cytokine productions on RAW264.7 cells were tested after preincubation with TLR-4 pathway inhibitors. The results indicated that DEG-PEI could facilitate the intranasal delivery of rAd5 vaccine. Both chemically linked (DP-RS09) and physically mixed RS09 (DP/RS09) could further enhance the mucosal immunity of rAd5 vaccine via TLR-4 pathway. This RS09 adjuvanted DEG-PEI polymer represents a potential intranasal vaccine delivery system and may have a wider application for other viral vectors.

Higher Frequency of NK and CD4+ T-Cells in Mucosa and Potent Cytotoxic Response in HIV Controllers

HIV infection induces immune alterations, mainly in gut mucosa, where the main target cells reside. However, the evolution of the infection is variable among infected individuals, as evidenced by HIV controllers who exhibit low or undetectable viral load in the absence of treatment. The aim of this study was to evaluate the frequency, phenotype and activity of T and NK cells in peripheral blood and gut mucosa in a cohort of Colombian HIV controllers. Blood and gut biopsies were included. The frequency and the activation status of T and NK cells were performed by flow cytometry. In addition, Gag-stimulated CD8⁺ T-cells and cytokine-stimulated NK cells were tested for cytotoxic activity. Finally, microbial translocation was measured by plasma lipopolysaccharide quantification. Compared with HIV-progressors, HIV controllers exhibited higher frequency of CD4⁺ T and NK cells, and lower expression of activation molecules in blood and mucosal immune cells, as well as lower microbial translocation. An increased production of molecules associated with cytotoxic activity of CD8⁺ T-cells in blood and mucosa and a higher percentage of polyfunctional CD8⁺ T cells in blood were also observed in HIV controllers. In addition, an increased activity of NK cells was observed in blood. These findings suggest that HIV controllers have a potent immune response, mainly mediated by cytotoxic cells that control HIV replication, which contribute to reducing alterations at the gut mucosa.

Nonneutralizing functional antibodies: a new "old" paradigm for HIV vaccines

Animal and human data from various viral infections and vaccine studies suggest that nonneutralizing antibodies (nNAb) without neutralizing activity in vitro may play an important role in protection against viral infection in vivo. This was illustrated by the recent human immunodeficiency virus (HIV) RV144 vaccine efficacy trial, which demonstrated that HIV-specific IgG-mediated nNAb directed against the V2 loop of HIV type 1 envelope (Env) were inversely correlated with risk for HIV acquisition, while Env-specific plasma IgA-mediated antibodies were directly correlated with risk. However, tier 1 NAb in the subset of responders with a low level of plasma Env-specific IgA correlated with decreased risk. Nonhuman primate simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus (SHIV) challenge studies suggest that Env-mediated antibodies are essential and sufficient for protection. A comparison of immune responses generated in human efficacy trials reveals subtle differences in the fine specificities of the antibody responses, in particular in HIV-specific IgG subclasses. The underlying mechanisms that may have contributed to protection against HIV acquisition in humans, although not fully understood, are possibly mediated by antibody-dependent cell-mediated cytotoxicity (ADCC) and/or other nonneutralizing humoral effector functions, such as antibody-mediated phagocytosis. The presence of such functional nNAb in mucosal tissues and cervico-vaginal and rectal secretions challenges the paradigm that NAb are the predominant immune response conferring protection, although this does not negate the desirability of evoking neutralizing antibodies through vaccination. Instead, NAb and nNAb should be looked upon as complementary or synergistic humoral effector functions. Several HIV vaccine clinical trials to study these antibody responses in various prime-boost modalities in the systemic and mucosal compartments are ongoing. The induction of high-frequency HIV-specific functional nNAb at high titers may represent an attractive hypothesis-testing strategy in future HIV vaccine efficacy trials.

HIV-1 vaccines: challenges and new perspectives

The development of a safe and effective preventive HIV-1 vaccine remains a public health priority. Despite scientific difficulties and disappointing results, HIV-1 vaccine clinical development has, for the first time, established proof-of-concept efficacy against HIV-1 acquisition and identified vaccine-associated immune correlates of risk. The correlate of risk analysis showed that IgG antibodies against the gp120 V2 loop correlated with decreased risk of HIV infection, while Env-specific IgA directly correlated with increased risk. The development of vaccine strategies such as improved envelope proteins formulated with potent adjuvants and DNA and vectors expressing mosaics, or conserved sequences, capable of eliciting greater breadth and depth of potentially relevant immune responses including neutralizing and non-neutralizing antibodies, CD4+ and CD8+ cell-mediated immune responses, mucosal immune responses, and immunological memory, is now proceeding quickly. Additional human efficacy trials combined with other prevention modalities along with sustained funding and international collaboration remain key to bring an HIV-1 vaccine to licensure.

A direct and nonredundant role for thymic stromal lymphopoietin on antiviral CD8 T cell responses in the respiratory mucosa

Mucosally produced thymic stromal lymphopoietin (TSLP) regulates Th2 responses by signaling to dendritic cells and CD4 T cells. Activated CD8 T cells express the TSLP receptor (TSLPR), yet a direct role for TSLP in CD8 T cell immunity in the mucosa has not been described. Because TSLP shares signaling components with IL-7, a cytokine important for the development and survival of memory CD8 T cells in systemic infection models, we hypothesized that TSLP spatially and nonredundantly supports the development of these cells in the respiratory tract. In this study, we demonstrate that influenza infection induces the early expression of TSLP by lung epithelial cells with multiple consequences. The global loss of TSLP responsiveness in TSLPR(-/-) mice enhanced morbidity and delayed viral clearance. Using a competitive adoptive transfer system, we demonstrate that selective loss of TSLPR signaling on antiviral CD8 T cells decreases their accumulation specifically in the respiratory tract as early as day 8 after infection, primarily due to a proliferation deficiency. Importantly, the subsequent persistence of memory cells derived from this pool was also qualitatively and quantitatively affected. In this regard, the local support of antiviral CD8 T cells by TSLP is well suited to the mucosa, where responses must be tempered to prevent excessive inflammation. Taken together, these data suggest that TSLP uniquely participates in local immunity in the respiratory tract and modulation of TSLP levels may promote long-term CD8 T cell immunity in the mucosa when other prosurvival signals are limiting.

Novel approaches in polyepitope T-cell vaccine development against HIV-1

RV144 clinical trial was modestly effective in preventing HIV infection. New alternative approaches are needed to design improved HIV-1 vaccines and their delivery strategies. One of these approaches is construction of synthetic polyepitope HIV-1 immunogen using protective T- and B-cell epitopes that can induce broadly neutralizing antibodies and responses of cytotoxic (CD8(+) CTL) and helpers (CD4(+) Th) T-lymphocytes. This approach seems to be promising for designing of new generation of vaccines against HIV-1, enables in theory to cope with HIV-1 antigenic variability, focuses immune responses on protective determinants and enables to exclude from the vaccine compound that can induce autoantibodies or antibodies enhancing HIV-1 infectivity. Herein, the authors will focus on construction and rational design of polyepitope T-cell HIV-1 immunogens and their delivery, including: advantages and disadvantages of existing T-cell epitope prediction methods; features of organization of polyepitope immunogens, which can generate high-level CD8(+) and CD4(+) T-lymphocyte responses; the strategies to optimize efficient processing, presentation and immunogenicity of polyepitope constructs; original software to design polyepitope immunogens; and delivery vectors as well as mucosal strategies of vaccination. This new knowledge may bring us a one step closer to developing an effective T-cell vaccine against HIV-1, other chronic viral infections and cancer.

A "prime-pull" vaccine strategy has a modest effect on local and systemic antibody responses to HIV gp140 in mice

One potential strategy for the prevention of HIV infection is to induce virus specific mucosal antibody that can act as an immune barrier to prevent transmission. The mucosal application of chemokines after immunisation, termed “prime-pull”, has been shown to recruit T cells to mucosal sites. We wished to determine whether this strategy could be used to increase B cells and antibody in the vaginal mucosa following immunisation with an HIV antigen. BALB/c mice were immunised intranasally with trimeric gp140 prior to vaginal application of the chemokine CCL28 or the synthetic TLR4 ligand MPLA, without antigen six days later. There was no increase in vaginal IgA, IgG or B cells following the application of CCL28, however vaginal application of MPLA led to a significant boost in antigen specific vaginal IgA. Follow up studies to investigate the effect of the timing of the “pull” stimulation demonstrated that when given 14 days after the initial immunisation MPLA significantly increased systemic antibody responses. We speculate that this may be due to residual inflammation prior to re-immunisation. Overall we conclude that in contrast to the previously observed effect on T cells, the use of “prime-pull” has only a modest effect on B cells and antibody.

Evolutionarily conserved epitopes on human immunodeficiency virus type 1 (HIV-1) and feline immunodeficiency virus reverse transcriptases detected by HIV-1-infected subjects

Anti-human immunodeficiency virus (HIV) cytotoxic T lymphocyte (CTL)-associated epitopes, evolutionarily conserved on both HIV type 1 (HIV-1) and feline immunodeficiency virus (FIV) reverse transcriptases (RT), were identified using gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) and carboxyfluorescein diacetate succinimide ester (CFSE) proliferation assays followed by CTL-associated cytotoxin analysis. The peripheral blood mononuclear cells (PBMC) or T cells from HIV-1-seropositive (HIV(+)) subjects were stimulated with overlapping RT peptide pools. The PBMC from the HIV(+) subjects had more robust IFN-γ responses to the HIV-1 peptide pools than to the FIV peptide pools, except for peptide-pool F3. In contrast, much higher and more frequent CD8(+) T-cell proliferation responses were observed with the FIV peptide pools than with the HIV peptide pools. HIV-1-seronegative subjects had no proliferation or IFN-γ responses to the HIV and FIV peptide pools. A total of 24% (40 of 166) of the IFN-γ responses to HIV pools and 43% (23 of 53) of the CD8(+) T-cell proliferation responses also correlated to responses to their counterpart FIV pools. Thus, more evolutionarily conserved functional epitopes were identified by T-cell proliferation than by IFN-γ responses. In the HIV(+) subjects, peptide-pool F3, but not the HIV H3 counterpart, induced the most IFN-γ and proliferation responses. These reactions to peptide-pool F3 were highly reproducible and persisted over the 1 to 2 years of testing. All five individual peptides and epitopes of peptide-pool F3 induced IFN-γ and/or proliferation responses in addition to inducing CTL-associated cytotoxin responses (perforin, granzyme A, granzyme B). The epitopes inducing polyfunctional T-cell activities were highly conserved among human, simian, feline, and ungulate lentiviruses, which indicated that these epitopes are evolutionarily conserved. These results suggest that FIV peptides could be used in an HIV-1 vaccine.

Electroporation mediated DNA vaccination directly to a mucosal surface results in improved immune responses

In vivo electroporation (EP) has been shown to be a highly efficient non-viral method for enhancing DNA vaccine delivery and immunogenicity, when the site of immunization is the skin or muscle of animals and humans. However, the route of entry for many microbial pathogens is via the mucosal surfaces of the human body. We have previously reported on minimally invasive, surface and contactless EP devices for enhanced DNA delivery to dermal tissue. Robust antibody responses were induced following vaccine delivery in several tested animal models using these devices. Here, we investigated extending the modality of the surface device to efficiently deliver DNA vaccines to mucosal tissue. Initially, we demonstrated reporter gene expression in the epithelial layer of buccal mucosa in a guinea pig model. There was minimal tissue damage in guinea pig mucosal tissue resulting from EP. Delivery of a DNA vaccine encoding influenza virus nucleoprotein (NP) of influenza H1N1 elicited robust and sustained systemic IgG antibody responses following EP-enhanced delivery in the mucosa. Upon further analysis, IgA antibody responses were detected in vaginal washes and sustained cellular immune responses were detected in animals immunized at the oral mucosa with the surface EP device. This data confirms that DNA delivery and EP targeting mucosal tissue directly results in both robust and sustainable humoral as well as cellular immune responses without tissue damage. These responses are seen both in the mucosa and systemically in the blood. Direct DNA vaccine delivery enhanced by EP in mucosa may have important clinical applications for delivery of prophylactic and therapeutic DNA vaccines against diseases such as HIV, HPV and pneumonia that enter at mucosal sites and require both cellular and humoral immune responses for protection.

Interaction between endogenous bacterial flora and latent HIV infection

Human commensal bacteria do not normally cause any diseases. However, in certain pathological conditions, they exhibit a number of curious behaviors. In HIV infection, these bacteria exhibit bidirectional relationships: whereas they cause opportunistic infections based on immunological deterioration, they also augment HIV replication, in particular, viral replication from latently infected cells, which is attributable to the effect of butyric acid produced by certain anaerobic bacteria by modifying the state of chromatin. Here, we review recent evidence supporting the contributory role of such endogenous microbes in disrupting HIV latency and its potential link to the clinical progression of AIDS.

Mucosal priming with a replicating-vaccinia virus-based vaccine elicits protective immunity to simian immunodeficiency virus challenge in rhesus monkeys

Mucosal surfaces are not targeted by most human immunodeficiency virus type 1 (HIV-1) vaccines, despite being major routes for HIV-1 transmission. Here we report a novel vaccination regimen consisting of a mucosal prime with a modified replicating vaccinia virus Tiantan strain (MVTT(SIVgpe)) and an intramuscular boost with a nonreplicating adenovirus strain (Ad5(SIVgpe)). This regimen elicited robust cellular immune responses with enhanced magnitudes, sustainability, and polyfunctionality, as well as higher titers of neutralizing antibodies against the simian immunodeficiency virus SIV(mac1A11) in rhesus monkeys. The reductions in peak and set-point viral loads were significant in most animals, with one other animal being protected fully from high-dose intrarectal inoculation of SIV(mac239). Furthermore, the animals vaccinated with this regimen were healthy, while ~75% of control animals developed simian AIDS. The protective effects correlated with the vaccine-elicited SIV-specific CD8(+) T cell responses against Gag and Pol. Our study provides a novel strategy for developing an HIV-1 vaccine by using the combination of a replicating vector and mucosal priming.

Lack of IL-7 and IL-15 signaling affects interferon-γ production by, more than survival of, small intestinal intraepithelial memory CD8+ T cells

Survival of antigen-specific CD8(+) T cells in peripheral lymphoid organs during viral infection is known to be dependent predominantly on IL-7 and IL-15. However, little is known about a possible influence of tissue environmental factors on this process. To address this question, we studied survival of memory antigen-specific CD8(+) T cells in the small intestine. Here, we show that 2 months after vaccinia virus infection, B8R(20-27) /H2-K(b) tetramer(+) CD8(+) T cells in the small intestinal intraepithelial (SI-IEL) layer are found in mice deficient in IL-15 expression. Moreover, SI-IEL and lamina propria lymphocytes do not express the receptor for IL-7 (IL-7Rα/CD127). In addition, after in vitro stimulation with B8R(20-27) peptide, SI-IEL cells do not produce high amounts of IFN-γ neither at 5 days nor at 2 months postinfection (p.i.). Importantly, the lack of IL-15 was found to shape the functional activity of antigen-specific CD8(+) T cells, by narrowing the CTL avidity repertoire. Taken together, these results reveal that survival factors, as well as the functional activity, of antigen-specific CD8(+) T cells in the SI-IEL compartments may markedly differ from their counterparts in peripheral lymphoid tissues.