Comparative study of the T cell response to two allelic forms of a malarial vaccine candidate protein.

T cell responses to two allelic forms of the merozoite surface Ag 2 (MSA2) of Plasmodium falciparum were mapped in mice using the rMSA2 proteins, Ag 1609 which has the sequence of the FCQ27/PNG strain and Ag 1615 which has the sequence of the Indochina 1 strain. Lymph node cells of BL/10 and B10.BR mice immunized with either Ag 1609 or Ag 1615 responded to both Ag in in vitro proliferation assays. Lymph node cells of BALB/c mice did not respond. The T cell determinants recognized by the responder strains were mapped to conserved and variant regions of these Ag using overlapping synthetic peptides. The determinants recognized by each mouse strain were distinct. Marked difference in sequence between the central regions of the two rMSA2 proteins did not affect antigenic processing of the conserved N and C terminal regions. Hence lymph node cells of BL/10 mice immunized with either Ag 1615 or Ag 1609 recognized an immunodominant T cell determinant at the highly conserved N terminal end within the sequence YSNTFINNAYNMSIR (peptide 3b) and B10.BR mice similarly immunized recognized an immunodominant determinant at the highly conserved C terminal within the sequence CTDGNKENCGAATSL (peptide 23). Several peptides identified as containing immunodominant T cell determinants specific to BL/10 mice induced peptide-specific T cells in both BL/10 and B10.BR mouse strains when used as immunogens. However, the ability of the peptide-primed T cells to proliferate in response to the rMSA2 proteins was confined to BL/10 mice. An example of this was observed with peptides 3b and N (KNESKYSNTFINNAYNMSIRRSMAN). Peptide N was able to prime B10.BR and BL/10 mice for an enhanced antibody response when these mice were subsequently immunized with Ag 1615 even though Ag 1615-specific T cell proliferation was not detected in B10.BR mice primed with N. The study concluded that 1) conserved sequences such as peptide N when used in vaccines may give rise to MSA2-specific memory Th cells amenable to boosting by subsequent exposure to all parasite strains and 2) peptide priming may be a useful pathway for inducing defined memory Th cells in a wider population and for preferentially inducing T dependent over T independent responses to some malarial Ag.     

Quantitative analysis of the immune response to mouse non-MHC transplantation antigens in vivo: the H60 histocompatibility antigen dominates over all others

Minor histocompatibility Ags (minor H Ags) are substantial impediments to MHC-matched solid tissue and bone marrow transplantation. From an antigenic standpoint, transplantation between MHC-matched individuals has the potential to be remarkably complex. To determine the extent to which the immune response is simplified by the phenomenon of immunodominance, we used peptide/MHC tetramers based on recently discovered minor H Ags (H60, H13, and HY) and monitored in vivo CD8 T cell responses of female C57BL/6 mice primed with MHC-matched, but background-disparate, male BALB.B cells. CD8 T cells against H60 overwhelmed responses to the H13 and HY throughout primary and secondary challenge. H60 immunodominance was an inherent quality, overcoming a lower memory precursor frequency compared with that of H13 and evoking a T cell response with diverse TCRV beta usage. IFN-gamma staining examining congenically defined minor H Ags extended H60 dominance over additional minor H Ags, H28, H4, and H7. These four minor H Ags accounted for up to 85% of the CD8 T cell response, but H60 stood out as the major contributor. These findings show that immunodominance applies to antigenically complex transplantation settings in vivo and that the responses to the H60 minor H Ag dominates in this model. We suggest that immunodominant minor H Ags are those that result from the absence of a self analog.     

Altered distribution of H60 minor H antigen-specific CD8 T cells and attenuated chronic vasculopathy in minor histocompatibility antigen mismatched heart transplantation in Cxcr3-/- mouse recipients

Chemokine-chemokine receptor interactions and the subsequent recruitment of T lymphocytes to the graft are believed to be among the initial events in the development of acute and chronic rejection of heart transplants. We sought to determine the role of chemokine receptor Cxcr3 on the development of acute and chronic rejection in a multiple minor Ag mismatched mouse heart transplant model. The frequencies and kinetics of immunodominant H60 (LTFNYRNL) miHA-specific CD8 T cells in wild-type or Cxcr3-/- C57BL/6 recipients were monitored using MHC class I tetramer after BALB/b donor hearts were transplanted. Acceptance of grafts, severity of rejection, and infiltration of T cells were not altered in Cxcr3-/- recipients. However, graft survival was moderately prolonged in Cxcr3-/- recipient mice undergoing acute rejection. Analyses of splenocytes, PBLs, and graft-infiltrating cells revealed increased alloreactive T cells (H60-specific CD8 T cells) in the peripheral blood and spleen but not in the graft. Adoptively transferred Cxcr3-/- CD8 T cells in the BALB/b heart-bearing B6 scid mice showed retention of alloreactive CD8 T cells in the blood but less infiltration into the graft. Cxcr3-/- recipients with long-term graft survival also showed a marked decrease of CD8+ T cell infiltration and reduced neo-intimal hyperplasia. These data indicate that Cxcr3 plays a critical role in the trafficking as well as activation of alloreactive T cells. This role is most eminent in a transplant model when a less complex inflammatory milieu is involved such as a well-matched graft and chronic rejection.     

Immune dysfunction associated with graft-vs-host reaction in mice transplanted across minor histocompatibility barriers. II. Reversible defect in T-dependent antibody responses

B cell and Th cell functions were assessed in mice undergoing a graft-vs-host reaction (GvHR) in response to minor histocompatibility Ag by using the plaque-forming cell (PFC) response to the T-independent Ag TNP-Brucella abortus and the T-dependent Ag TNP-SRBC. Bone marrow plus spleen cells from B10.D2 mice were transplanted into lethally irradiated B10.D2 (syngeneic recipient) or H-2d-compatible BALB/c (allogeneic recipient) to produce a chronic form of GvHR. BALB/c recipients of an allogeneic transplant demonstrated a marked and proportional lymphoid depletion of the spleen with normal percentages of B cells, T cells, and CD4+ and CD8+ T cell subsets. Mice with GvHR made normal numbers of PFC/10(5) spleen cells in response to the T-independent Ag, but a significantly depressed number of PFC/10(5) spleen cells to the T-dependent Ag compared with normal B10.D2 mice and with irradiated B10.D2 recipients of syngeneic B10.D2 marrow plus spleen cells. Mice undergoing the minor Ag GvHR made significantly larger numbers of PFC/10(5) spleen cells after secondary immunization with TNP-SRBC compared with controls. In vitro assays demonstrated that B cells from mice with GvHR responded to T help from normal B10.D2 mice and that T cells from mice with GvHR provided help to normal B cells after in vivo immunization. These data demonstrate that radiation chimeras with GvHR in response to minor histocompatibility Ag have relatively normal B cell function and an apparent defect in T helper cell function that is reversible by immunization with appropriate Ag.     

Immunologic Control of Mus musculus Papillomavirus Type 1

Persistent papillomas developed in ~10% of out-bred immune-competent SKH-1 mice following MusPV1 challenge of their tail, and in a similar fraction the papillomas were transient, suggesting potential as a model. However, papillomas only occurred in BALB/c or C57BL/6 mice depleted of T cells with anti-CD3 antibody, and they completely regressed within 8 weeks after depletion was stopped. Neither CD4+ nor CD8+ T cell depletion alone in BALB/c or C57BL/6 mice was sufficient to permit visible papilloma formation. However, low levels of MusPV1 were sporadically detected by either genomic DNA-specific PCR analysis of local skin swabs or in situ hybridization of the challenge site with an E6/E7 probe. After switching to CD3+ T cell depletion, papillomas appeared upon 14/15 of mice that had been CD4+ T cell depleted throughout the challenge phase, 1/15 of CD8+ T cell depleted mice, and none in mice without any prior T cell depletion. Both control animals and those depleted with CD8-specific antibody generated MusPV1 L1 capsid-specific antibodies, but not those depleted with CD4-specific antibody prior to T cell depletion with CD3 antibody. Thus, normal BALB/c or C57BL/6 mice eliminate the challenge dose, whereas infection is suppressed but not completely cleared if their CD4 or CD8 T cells are depleted, and recrudescence of MusPV1 is much greater in the former following treatment with CD3 antibody, possibly reflecting their failure to generate capsid antibody. Systemic vaccination of C57BL/6 mice with DNA vectors expressing MusPV1 E6 or E7 fused to calreticulin elicits potent CD8 T cell responses and these immunodominant CD8 T cell epitopes were mapped. Adoptive transfer of a MusPV1 E6-specific CD8+ T cell line controlled established MusPV1 infection and papilloma in RAG1-knockout mice. These findings suggest the potential of immunotherapy for HPV-related disease and the importance of host immunogenetics in the outcome of infection.     

Primary vascularization of the graft determines the immunodominance of murine minor H antigens during organ transplantation

Grafts can be rejected even when matched for MHC because of differences in the minor histocompatibility Ags (mH-Ags). H4- and H60-derived epitopes are known as immunodominant mH-Ags in H2(b)-compatible BALB.B to C57BL/6 transplantation settings. Although multiple explanations have been provided to explain immunodominance of Ags, the role of vascularization of the graft is yet to be determined. In this study, we used heart (vascularized) and skin (nonvascularized) transplantations to determine the role of primary vascularization of the graft. A higher IFN-γ response toward H60 peptide occurs in heart recipients. In contrast, a higher IFN-γ response was generated against H4 peptide in skin transplant recipients. Peptide-loaded tetramer staining revealed a distinct antigenic hierarchy between heart and skin transplantation: H60-specific CD8(+) T cells were the most abundant after heart transplantation, whereas H4-specific CD8(+) T cells were more abundant after skin graft. Neither the tissue-specific distribution of mH-Ags nor the draining lymph node-derived dendritic cells correlated with the observed immunodominance. Interestingly, non-primarily vascularized cardiac allografts mimicked skin grafts in the observed immunodominance, and H60 immunodominance was observed in primarily vascularized skin grafts. However, T cell depletion from the BALB.B donor prior to cardiac allograft induces H4 immunodominance in vascularized cardiac allograft. Collectively, our data suggest that immediate transmigration of donor T cells via primary vascularization is responsible for the immunodominance of H60 mH-Ag in organ and tissue transplantation.     

Generation of helper cell-independent cytotoxic T lymphocytes is dependent upon L3T4+ helper T cells

The role of L3T4+ (CD4+) Th cells in generation of CTL specific for discrete minor histocompatibility Ag was investigated. Suppression of the function of Th cells in vivo by chronic treatment with anti-L3T4 mAb prevented congenic strains of mice from being primed and from generating CTL specific for Ag encoded by the minor histocompatibility loci--H-3, H-1, and B2m. Analysis of proliferative responses and lymphokine secretion of cells from animals primed with one of these minor H Ag, beta 2-microglobulin, but not treated with anti-L3T4 antibodies, indicated that L3T4- class I MHC-restricted T cells were themselves responsible for the very great majority of the observed minor H Ag-specific proliferation and secretion of lymphokines associated with both T cell proliferation and activation of CTL. All together, the data indicate that in responses against discrete minor H Ag, L3T4+Th-independent CTL are generated through an L3T4+Th-dependent pathway.     

Inefficient cross-presentation limits the CD8+ T cell response to a subdominant tumor antigen epitope

CD8(+) T lymphocytes (T(CD8)) responding to subdominant epitopes provide alternate targets for the immunotherapy of cancer, particularly when self-tolerance limits the response to immunodominant epitopes. However, the mechanisms that promote T(CD8) subdominance to tumor Ags remain obscure. We investigated the basis for the lack of priming against a subdominant tumor epitope following immunization of C57BL/6 (B6) mice with SV40 large tumor Ag (T Ag)-transformed cells. Immunization of B6 mice with wild-type T Ag-transformed cells primes T(CD8) specific for three immunodominant T Ag epitopes (epitopes I, II/III, and IV) but fails to induce T(CD8) specific for the subdominant T Ag epitope V. Using adoptively transferred T(CD8) from epitope V-specific TCR transgenic mice and immunization with T Ag-transformed cells, we demonstrate that the subdominant epitope V is weakly cross-presented relative to immunodominant epitopes derived from the same protein Ag. Priming of naive epitope V-specific TCR transgenic T(CD8) in B6 mice required cross-presentation by host APC. However, robust expansion of these T(CD8) required additional direct presentation of the subdominant epitope by T Ag-transformed cells and was only significant following immunization with T Ag-expressing cells lacking the immunodominant epitopes. These results indicate that limited cross-presentation coupled with competition by immunodominant epitope-specific T(CD8) contributes to the subdominant nature of a tumor-specific epitope. This finding has implications for vaccination strategies targeting T(CD8) responses to cancer.     

Examination of HY response: T cell expansion, immunodominance, and cross-priming revealed by HY tetramer analysis

We have applied MHC class I tetramers representing the two H2(b) MHC class I-restricted epitopes of the mouse male-specific minor transplantation Ag, HY, to directly determine the extent of expansion and immunodominance within the CD8+ T cell compartment following exposure to male tissue. Immunization with male bone marrow (BM), spleen, dendritic cells (DCs) and by skin graft led to rapid expansion of both specificities occupying up to >20% of the CD8+ T cell pool. At a high dose, whole BM or spleen were found to be more effective at stimulating the response than BM-derived DCs. In vivo, immunodominance within the responding cell population was only observed following chronic Ag stimulation, whereas epitope immunodominance was established rapidly following in vitro restimulation. Peptide affinity for the restricting MHC molecule was greater for the immunodominant epitope, suggesting that this might be a factor in the emergence of immunodominance. Using tetramers, we were able to directly visualize the cross-primed CD8+ HY response, but we did not find it to be the principal route for MHC class I presentation. Immunization with female spleen or DCs coated with the full complement of defined HY peptides, including the A(b)-restricted CD4+ Th cell determinant, failed to induce tetramer-reactive cells.     

Immunodominance in the graft-vs-host disease T cell response to minor histocompatibility antigens

Immunodominance controls the generation of CTL in the C57BL/6By (B6) anti-BALB.B H-2b-matched strain combination. Despite the potential of responding to numerous individual minor histocompatibility (H) Ag on BALB.B APC, the focus of the CTL response is largely specific for only a limited number of target Ag. These minor H Ag could be distinguished by their differential expression on a panel of target cells from the CXB recombinant inbred strains, the E, G, I, J, and K (all H-2b), which express different composites of the original BALB minor H Ag. A hierarchy was observed in which first-order immunodominant Ag were present on both CXBK and CXBG cells, whereas second-order dominant Ag were found on CXBE, CXBJ, and CXBI cells. To test whether immunodominance also plays a role in the development of lethal graft-vs-host disease (GVHD) directed to multiple minor H Ag, B6 T cells were transplanted along with T cell depleted bone marrow, to irradiated (825 rad) recipients of either the BALB.B or CXB recombinant inbred strains. The results indicate that a hierarchy of immunodominance does exist in GVHD, but it differs from that predicted from the in vitro CTL studies. GVHD was observed in BALB.B, CXBE, CXBI, and CXBJ recipients, but not in CXBG and CXBK recipients. Presensitization of B6 donor mice to CXBG or CXBK splenocytes 3 wk before transplant did not significantly increase the overall GVHD potential in the corresponding CXBG or CXBK recipients. Evidence for second-order immunodominance was provided by the transfer of CXBE T cells and ATBM to irradiated CXBG and BALB.B recipients with resultant, potent GVHD.     

A single-amino-acid variant of the H60 CD8 epitope generates specific immunity with diverse TCR recruitment

TCR of CD8 T cells recognizes peptides of 8–9 amino acids in length (epitope) complexed with MHC class I. Peptide ligands differing from an epitope by one or two amino acids are thought to modulate the immune response specific to that epitope. H60 is a minor histocompatibility antigen for which the specific CD8 T-cell response dominates during alloresponse after MHC-matched allogeneic transplantation. In the present study, we developed a transgenic mouse (designated H60H Tg) expressing a variant of H60, designated H60H, in which the arginine residue at position 4 of the H60 epitope sequence (LTFNYRNL) is replaced by a histidine residue (LTFHYRNL). Immunization of female C57BL/6 mice with splenocytes from male H60H Tg induced a CD8 T cell primary response and memory response after re-challenge. The response was CD4 help-dependent, demonstrating the potency of H60H as a cellular antigen. The response induced by the H60H cellular antigen was comparable to that induced by H60 in its peak magnitude and overall immune kinetics. H60H challenge recruited broadly diverse TCRs to the specific response, shaping a TCR repertoire different from that of the natural H60 epitope. However, some of the TCRs did overlap between the H60H- and H60-specific CD8 T cells, suggesting that H60H might modulate the H60-specific response. These results may provide a basis for the modulation of the H60-specific CD8 T-cell response.     

T cells targeted against a single minor histocompatibility antigen can cure solid tumors

T cells responsive to minor histocompatibility (H) antigens are extremely effective in curing leukemia but it remains unknown whether they can eradicate solid tumors. We report that injection of CD8(+) T cells primed against the immunodominant H7(a) minor H antigen can cure established melanomas in mice. Tumor rejection was initiated by preferential extravasation at the tumor site of interferon (IFN)-gamma-producing H7(a)-specific T cells. Intratumoral release of IFN-gamma had two crucial effects: inhibition of tumor angiogenesis and upregulation of major histocompatibility complex (MHC) class I expression on tumor cells. Despite ubiquitous expression of H7(a), dissemination of a few H7(a)-specific T cells in extralymphoid organs caused neither graft-versus-host disease (GVHD) nor vitiligo because host nonhematopoietic cells were protected by their low expression of MHC class I. Our preclinical model yields unique insights into how minor H antigen-based immunotherapy could be used to treat human solid tumors.     

A recombinant malaria protein that can induce Th1 and CD8+ T cell responses without antibody formation.

Inbred strains of mice were immunized with p190-3, a 38-kDa recombinant protein derived from p190, a major merozoite surface Ag of the malaria parasite Plasmodium falciparum. Ag-specific proliferative T cell responses were obtained in H-2b, H-2d, and H-2k mouse strains. Surprisingly, mice of the H-2b haplotype (e.g., C57BL/6) did not give a measurable antibody response to the recombinant protein administered in Freund's adjuvant, but CD8+/CD4- as well as CD4+/CD8- T cells specific for p190-3 could be obtained after in vivo priming and in vitro selection with Ag. Distinct epitopes of p190-3 recognized by the CD8+ and CD4+ T cells from C57BL/6 mice were identified. The CD8+ T cells could kill H-2b APC in the presence of the appropriate epitope-containing peptide. The p190-3-specific CD4+ cells isolated from C57BL/6 mice were of the Th1 type. In contrast, Th2 cells, but no CD8+ T cells were present in a p190-3-specific line from BALB/c mice, which give good antibody responses to p190-3.     

Robust antigen specific th17 T cell response to group A Streptococcus is dependent on IL-6 and intranasal route of infection

Group A streptococcus (GAS, Streptococcus pyogenes) is the cause of a variety of clinical conditions, ranging from pharyngitis to autoimmune disease. Peptide-major histocompatibility complex class II (pMHCII) tetramers have recently emerged as a highly sensitive means to quantify pMHCII-specific CD4+ helper T cells and evaluate their contribution to both protective immunity and autoimmune complications induced by specific bacterial pathogens. In lieu of identifying an immunodominant peptide expressed by GAS, a surrogate peptide (2W) was fused to the highly expressed M1 protein on the surface of GAS to allow in-depth analysis of the CD4+ helper T cell response in C57BL/6 mice that express the I-A(b) MHCII molecule. Following intranasal inoculation with GAS-2W, antigen-experienced 2W:I-A(b)-specific CD4+ T cells were identified in the nasal-associated lymphoid tissue (NALT) that produced IL-17A or IL-17A and IFN-γ if infection was recurrent. The dominant Th17 response was also dependent on the intranasal route of inoculation; intravenous or subcutaneous inoculations produced primarily IFN-γ+ 2W:I-A(b+) CD4+ T cells. The acquisition of IL-17A production by 2W:I-A(b)-specific T cells and the capacity of mice to survive infection depended on the innate cytokine IL-6. IL-6-deficient mice that survived infection became long-term carriers despite the presence of abundant IFN-γ-producing 2W:I-A(b)-specific CD4+ T cells. Our results suggest that an imbalance between IL-17- and IFN-γ-producing CD4+ T cells could contribute to GAS carriage in humans.     

H2-M3-restricted CD8+ T cells induced by peptide-pulsed dendritic cells confer protection against Mycobacterium tuberculosis

One of the oligopolymorphic MHC class Ib molecules, H2-M3, presents N-formylated peptides derived from bacteria. In this study, we tested the ability of an H2-M3-binding peptide, TB2, to induce protection in C57BL/6 mice against Mycobacterium tuberculosis. Immunization with bone marrow-derived dendritic cell (BMDC) pulsed with TB2 or a MHC class Ia-binding peptide, MPT64(190-198) elicited an expansion of Ag-specific CD8+ T cells in the spleen and the lung. The number of TB2-specific CD8+ T cells reached a peak on day 6, contracted with kinetics similar to MPT64(190-198)-specific CD8+ T cells and was maintained at an appreciable level for at least 60 days. The TB2-specific CD8+ T cells produced less effector cytokines but have stronger cytotoxic activity than MPT64(190-198)-specific CD8+ T cells. Mice immunized with TB2-pulsed BMDC as well as those with MPT64(190-198)-pulsed BMDC showed significant protection against an intratracheal challenge with M. tuberculosis H37Rv. However, histopathology of the lung in mice immunized with TB2-pulsed BMDC was different from mice immunized with MPT64(190-198)-pulsed BMDC. Our results suggest that immunization with BMDC pulsed with MHC class Ib-restricted peptides would be a useful vaccination strategy against M. tuberculosis.     

Induction of obliterative airway disease in murine tracheal allografts by CD8+ CTLs recognizing a single minor histocompatibility antigen

The role of minor histocompatibility Ag (mHAg)-specific CD8+ CTLs in the pathogenesis of chronic lung allograft rejection (bronchiolitis obliterans syndrome) remains to be elucidated. Thus, the goal of this study was to define the role of a single mHAg mismatch at the polymorphic H13 allele in the development of obliterative airway disease (OAD) after murine heterotopic tracheal transplantation. The H13a and H13b alleles encode for the SSVVGVWYL (SVL9) and SSVIGVWYL (SIL9) mHAgs, respectively, presented in the context of the H2Db MHC class I molecule. Toward this, C56BL/10SnJ (H13a) tracheal allografts were transplanted into congenic B10.CE-H13b Aw(30NX)/Sn (H13b) recipients. The allografts were harvested at 30, 60, and 90 days after transplantation, and OAD lesions (epithelial damage, cellular infiltration, and luminal fibrosis) were confirmed histologically. Selected groups of mice were immunized (s.c.) or tolerized (i.v.) with the SVL9 peptide before transplantation. This single mHAg mismatch induced the development of OAD within 90 days. SVL9 immunization significantly accelerated the kinetics of the OAD lesions. In contrast, SVL9 tolerization completely abrogated the development of OAD. This was correlated with a complete abrogation of H13a-specific CD8+ CTL responses with a significant reduction in the frequency of IFN-gamma-producing CTLs and the activation of TGF-beta-producing CD8+ T cells. In conclusion, a single mHAg mismatch can induce the development of OAD. These data also suggest that mHAg-reactive CD8+ CTLs may play an important role in the pathogenesis of chronic lung allograft rejection in humans.     

MHC-independent genetic factors control the magnitude of CD4+ T cell responses to amyloid-β peptide in mice through regulatory T cell-mediated inhibition

Accumulation of amyloid-β peptide (Aβ) is considered the triggering factor of pathogenic lesions in Alzheimer's disease (AD), and vaccines targeting Aβ are promising therapeutic options. However, the occurrence of meningoencephalitides attributed to T cell responses in 6% of Aβ-immunized patients underscores the need for a better understanding of T cell responses to Aβ. We characterized the parameters controlling the magnitude of Aβ-specific CD4(+) T cell responses in mice. T cell responsiveness to Aβ1-42 was highly heterogeneous between mouse strains of different H-2 haplotypes, with SJL/J (H-2(s)) mice displaying a strong response, mainly specific for Aβ10-24, and C57BL/6 (H-2(b)) mice displaying a weak response to Aβ16-30. Surprisingly, C57BL/6 mice congenic for the H-2(s) haplotype (B6.H-2(S)), which display a "permissive" MHC class II allele for presentation of the immunodominant Aβ10-24 epitope, showed a very weak CD4(+) T cell response to Aβ, suggesting that MHC-independent genes downmodulate Aβ-specific CD4(+) T cell responses in C57BL/6 background. Vaccine-induced CD4(+) T cell responses to Aβ were significantly enhanced in both C57BL/6 and B6.H-2(S) mice upon depletion of regulatory T cells (Tregs), whereas Treg-depleted SJL/J mice displayed unaltered Aβ-specific T cell responses. Finally, Treg depletion in C57BL/6 transgenic APPPS1 mice, a mouse model of AD, results in enhanced vaccine-induced CD4(+) T cell responses in AD compared with wild-type animals. We concluded that the magnitude of Aβ-specific CD4(+) T cell responses is critically controlled in both physiological and pathological settings by MHC-independent genetic factors that determine the overall potency of Aβ-specific Treg responses.     

Cutting edge: the minor histocompatibility antigen H60 peptide interacts with both H-2Kb and NKG2D

Minor histocompatibility Ags elicit cell-mediated immune responses and graft rejection in individuals receiving MHC-matched tissues. H60 represents a dominant Ag that elicits a strong CTL response in C57BL/6 mice immunized against BALB.B. An 8-aa peptide in the H60 protein is presented by H-2K(b) and this is recognized by the TCR as an alloantigen. The intact H60 glycoprotein is a ligand for the costimulatory NKG2D receptor that is expressed by activated CD8(+) T cells. Thus, H60 may provide both an allogeneic peptide and its own costimulation. We show that mutation of an H-2K(b)-binding anchor residue in the H60 peptide completely abrogates binding of H60 glycoprotein to NKG2D and a synthetic H60 peptide partially blocks the binding of NKG2D to its ligand. Ligands of the human NKG2D receptor are remarkably polymorphic, suggesting that these may also serve as minor histocompatibility Ags.     

CD4+ T cell clones specific for the human p97 melanoma-associated antigen can eradicate pulmonary metastases from a murine tumor expressing the p97 antigen.

p97 is a human tumor-associated Ag present on most melanoma cells that represents a possible target for immunologic attack. To evaluate the capacity of T cells reactive with this protein to promote elimination of melanoma cells expressing p97, a murine model was developed by transfecting a C3H/HeN melanoma with the p97 cDNA, generating p97-specific CD4+ T cells by in vivo immunization of C3H/HeN mice with a vaccinia/p97 recombinant virus followed by in vitro cloning with soluble p97 protein, and determining whether these CD4+ T cells could mediate rejection of pulmonary metastases. Characterization of the T cell clones demonstrated the presence of both I-Ak and I-Ek-restricted clones, although the majority of clones recognized p97 in the context of I-Ek. Analysis of clonal specificity using truncated p97 proteins revealed that at least three epitopes were immunogenic, and further studies with overlapping 15-amino acid peptides from a region of the p97 molecule defined by these truncated proteins identified an immunodominant epitope responsible for the majority of the I-Ek response. The T cell clones were not capable of directly recognizing the p97-expressing melanoma cells but responded to the tumor if syngeneic APC were present to process the tumor-derived p97 Ag. The therapeutic efficacy of these CD4+ T cell clones was evaluated in an adoptive therapy model in which mice bearing metastatic pulmonary lesions were treated by i.v. administration of the p97-specific cells. Despite the inability of the CD4+ clones to directly respond to or lyse the tumor cells, the clones were effective in promoting tumor eradication. In vitro studies demonstrated that this may have reflected secretion of lymphokines that activated macrophages to lyse the tumor. The results suggest that noncytolytic p97-specific CD4+ T cell clones can be effective in therapy of pulmonary melanoma metastases. Moreover, if human T cells reactive with the p97 protein could be generated, the expression of this tumor-associated Ag in melanoma cells might be adequate for such T cells to mediate a therapeutic antitumor response.     

Specificity of the mouse cytotoxic T lymphocyte response to adenovirus 5. E1A is immunodominant in H-2b, but not in H-2d or H-2k mice

The Ag specificity and MHC restriction of the CTL response to adenovirus 5 (Ad5) in three strains of mice, C57BL/10 (H-2b), BALB/c (H-2d), and C3H/HeJ (H-2k), were tested. Polyclonal Ad5-specific CTL were prepared by priming mice in vivo with live Ad5 virus followed by secondary in vitro stimulation of the spleen cells with virus-infected syngeneic cells. The Ad5-specific CTL were Db restricted in C57BL/10 and Kk restricted in C3H/HeJ. In BALB/c mice both Kd- and Dd/Ld-restricted CTL were detected. The polyclonal Ad5-specific CTL response in C57BL/10 mice is directed exclusively against the products of the E1A region, which comprises only 5% of the Ad5 genome. In BALB/c mice E1A is at best a very minor target Ag and in C3H/HeJ mice E1A is not recognized at all. Using the H-2 congenic mouse strains B10.BR (H-2k) and C3H.SW (H-2b) it was shown that the immunodominance of E1A is H-2 dependent. The 19-kDa glycoprotein encoded in the E3 region of Ad5, which binds to class I MHC in the endoplasmic reticulum and prevents its translocation to the cell surface, does not affect the specificity of the CTL response in C57BL/10 mice toward E1A. However, it affects the MHC restriction of the Ad5-specific response in BALB/c mice, selectively inhibiting generation of Kd-restricted CTL.