Ruben Dyall

A Single Heteroclitic Epitope Determines Cancer Immunity After Xenogeneic DNA Immunization Against a Tumor Differentiation Antigen

Successful active immunization against cancer requires induction of immunity against self or mutated self Ags. However, immunization against self Ags is difficult. Xenogeneic immunization with orthologous Ags induces cancer immunity. The present study evaluated the basis for immunity induced by active immunization against a melanoma differentiation Ag, gp100. Tumor rejection of melanoma was assessed after immunization with human gp100 (hgp100) DNA compared with mouse gp100 (mgp100). C57BL/6 mice immunized with xenogeneic full-length hgp100 DNA were protected against syngeneic melanoma challenge. In contrast, mice immunized with hgp100 DNA and given i.p. tolerizing doses of the hgp100 Db-restricted peptide, hgp10025–33, were incapable of rejecting tumors. Furthermore, mice immunized with DNA constructs of hgp100 in which the hgp10025–27 epitope was substituted with the weaker Db-binding epitope from mgp100 (mgp10025–27) or a mutated epitope unable to bind Db did not reject B16 melanoma. Mice immunized with a minigene construct of hgp10025–33 rejected B16 melanoma, whereas mice immunized with the mgp10025–33 minigene did not develop protective tumor immunity. In this model of xenogeneic DNA immunization, the presence of an hgp100 heteroclitic epitope with a higher affinity for MHC created by three amino acid (25 to 27) substitutions at predicted minor anchor residues was necessary and sufficient to induce protective tumor immunity in H-2b mice with melanoma.

Age-Related Dysregulation in CD8 T Cell Homeostasis: Kinetics of a Diversity Loss

Relative diversity and representation of peripheral T cells bearing different TCR Vβ families are remarkably tightly regulated between birth and advanced adulthood. By contrast, individual elderly humans and C3H.SW and B10.BR aged mice display drastic disruption in such regulation. It was suggested that the alterations in the murine aged T cell compartment were due to age-related clonal T cell expansions (TCE). Here, we studied the kinetics of homeostatic dysregulation of T cell populations in aged C57BL/6 (B6) mice. Using mAb staining, we show that the percentages of αβ+CD8+ or CD4+ T cells bearing different TCRVβ elements remain virtually constant in mice up to 12 mo of age. In 22-mo-old mice, however, there is a dramatic disturbance of this pattern owing to the emergence of CD8+ TCE. Expanded T cells did not show any obvious bias in Vβ usage and were derived in all cases examined thus far from a single clone. TCE appeared later in life, compared with B cell clonal expansions. However, and in contrast to those detected in humans, TCE were frequently unstable disappearing within 2–4 mo, with other TCE appearing within the same time frame. Additional studies carried on thymic T cells, thymectomized mice, and young T transferred cells into Rag1−/− mice suggest that the clonal expansions occur in the periphery and that their onset is accelerated by decreased thymic output and/or function(s).

Cellular requirements for the monoclonal antibody‐mediated eradication of an established solid tumor

Following subcutaneous implantation, the murine lymphoma E.G7 [a variant of EL‐4, transfected with the chicken ovalbumin (OVA) gene] up‐regulates the CD4 molecule. We previously showed that the administration of an anti‐CD4 monoclonal antibody (mAb) to EG.7‐bearing mice leads to a rapid and complete regression of large established tumors. This tumor regression was shown to require both CD8+ cells and functional Fcγ receptors (FcγR), as it failed to occur in mice depleted of CD8 cells, or mice genetically deficient in FcγRI/III (γ− / − mice). Using adoptive transfer, we now show that the FcγR + cells required for this regression are the CD11b+ (phagocytic) cells. Furthermore, experiments using peptide tolerization demonstrated that the critical CD8 CTL population in this model is tumor specific. Analysis of tumors at various stages of regression revealed a massive CD11b+ FcγR + and a marginal CD8 infiltration. In the presence of the CTL determinant OVA‐8 on tumor cells and of the antitumor mAb, this CD8 infiltration became remarkable, and correlated with tumor regression. These results identify the specific cellular effectors essential for the mAb‐mediated tumor regression, and suggest that FcγR‐activated macrophages induced an expansion of tumor‐eliminating CTL in situ.

MHC Polymorphism Can Enrich the T Cell Repertoire of the Species by Shifts in Intrathymic Selection

The murine class I molecule H-2Kb and its natural gene conversion variant, H-2Kbm8, which differs from H-2Kb solely at 4 aa at the bottom of the peptide-binding B pocket, are expressed in coisogenic mouse strains C57BL/6 (B6) and B6.C-H-2bm8 (bm8). These two strains provide an excellent opportunity to study the effects of Mhc class I polymorphism on the T cell repertoire. We recently discovered a gain in the antiviral CTL repertoire in bm8 mice as a consequence of the emergence of the Mhc class I allele H-2Kbm8. In this report we sought to determine the mechanism behind the generation of this increased CTL diversity. Our results demonstrate that repertoire diversification occurred by a gain in intrathymic positive selection. As previously shown, the emergence of the same Mhc allele also caused a loss in positive selection of T cell repertoire specific for another Ag, OVA-8. This indicates that a reciprocal loss-and-gain pattern of intrathymic selection exists between H-2Kb and H-2Kbm8. Therefore, in the thymus of an individual, a new Mhc allele can select new T cell specificities, while abandoning some T cell specificities selected by the wild-type allele. A byproduct of this repertoire shift is a net gain of T cell repertoire of the species, which is likely to improve its survival fitness.