Combined anti-CD40 conditioning and well-timed immunization prolongs CD8+ T cell accumulation and control of established brain tumors.

Adoptive cell transfer has been shown to significantly reduce established tumors in both experimental models and cancer patients. Owing to the tolerogenic nature of cancer, approaches that lead to durable maintenance of functional T cells in tumor-bearing hosts are needed to maximize tumor regression. In this study, we investigated strategies to augment CD8+ T-cell (T-CD8)-mediated adoptive immunotherapy of mice bearing advanced-stage autochthonous brain tumors by targeting a weakly immunogenic epitope. We found that immunization enhanced the accumulation of adoptively transferred T-CD8 at the tumor site, but that the timing of immunization was critical for optimal T cell expansion. A more rapid accumulation of T-CD8 was achieved when mice were conditioned with agonist anti-CD40 antibody before adoptive transfer due to increased T cell activation against the endogenous tumor antigen. Both approaches led to an increase in the lifespan of SV11 mice due to decreased tumor progression. However, tumor-specific T-CD8 did not persist long term at the tumor site after administration of either regimen. Importantly, the combination of anti-CD40 conditioning followed by optimally timed immunization synergistically promoted long-term maintenance of T-CD8 in the brain and dramatically enhanced survival. A second round of combination immunotherapy resulted in a further increase in survival, suggesting long-term tumor sensitivity to CD8+ T-cell-based immunotherapy. These results demonstrate that even a weak antigen can be effectively targeted for control of established tumors using a combined adoptive transfer plus immune modulation approach and suggest that similar strategies may translate to clinical practice.

Accumulation of CD8+ T cells in advanced-stage tumors and delay of disease progression following secondary immunization against an immunorecessive epitope.

Self-reactive T cells that survive the process of positive and negative selection during thymocyte development represent potential effector cells against tumors that express these same self-Ags. We have previously shown that CD8+ T lymphocytes (T(CD8)) specific for an immunorecessive epitope, designated epitope V, from the SV40 large T Ag (Tag) escape thymic deletion in line SV11 Tag-transgenic mice. In contrast, these mice are tolerant to the three most dominant Tag epitopes. The majority of the residual epitope V-specific T(CD8) have a low avidity for the target epitope, but a prime/boost regimen can expand higher avidity clones in vivo. Whether higher avidity T(CD8) targeting this epitope are affected by Tag-expressing tumors in the periphery or can be recruited for control of tumor progression remains unknown. In the current study, we determined the fate of naive TCR-transgenic T(CD8) specific for Tag epitope V (TCR-V cells) following transfer into SV11 mice bearing advanced-stage choroid plexus tumors. The results indicate that TCR-V cells are rapidly triggered by the endogenous Tag and acquire effector function, but fail to accumulate within the tumors. Primary immunization enhanced TCR-V cell frequency in the periphery and promoted entry into the brain, but a subsequent booster immunization caused a dramatic accumulation of TCR-V T cells within the tumors and inhibited tumor progression. These results indicate that epitope V provides a target for CD8+ T cells against spontaneous tumors in vivo, and suggests that epitopes with similar properties can be harnessed for tumor immunotherapy.

Stromal cells provide the matrix for migration of early lymphoid progenitors through the thymic cortex.

During steady state lymphopoiesis in the postnatal thymus, migration of precursors outward from the deep cortex toward the capsule is required for normal differentiation. Such migration requires, at a minimum, expression of adhesive receptors on the migrating lymphoid cells, as well as a stable matrix of their ligands persisting throughout the region of migration. In this study, we address the nature of this adhesive matrix. Although some precursor stages bound efficiently to extracellular matrix ligands, a specific requirement for the cell surface ligand VCAM-1 was also found. In situ analysis revealed that early precursors are found in intimate contact with a matrix formed by stromal cells in the cortex, a proportion of which expresses VCAM-1. In vivo administration of an anti-VCAM-1 Ab resulted in decreased thymic size and altered distribution of early precursors within the cortex. These results indicate that precursors migrating outward through the cortex may use a cellular, rather than extracellular, matrix for adhesion, and suggest that the VCAM-1(+) subset of cortical stroma may play a crucial role in supporting the migration of early precursors in the steady state thymus.