Donor CD8+ T Cells Facilitate Graft-Versus-Tumor Effect Via Alloantigen Rather Than Tumor-Specific Antigen Recognition Following Murine Myeloablative BMT.

Previous data from our group and others has shown that donor CD8+ Tcells mediate graft-versus-tumor (GVT) function in murine myeloablative bone marrow transplantation (BMT) via Perforin/Fas ligand-dependent mechanisms. However, there has to date been no analysis of the mechanism of tumor recognition (i.e allo- versus tumor-specific antigen recognition) by donor CD8+ T cells following myeloablative MHC-mismatched BMT. In order to test the hypothesis that donor CD8 T-cells require allo-antigen recognition to maintain graft-versus-tumor effect, we developed stable full chimeras by transplanting T-cell depleted bone marrow (TCD BM) from C57BL/6 (H-2^b) donor mice into myeloablated BALB/c (H-2^d) hosts given 800 cGy total body irradiation (TBI) and evaluated the in vivo ability of CD8+ TCR+ splenocytes from these donors to kill the BCL₁ tumor (a BALB/c-derived B-cell lymphoma carrying a detectable tumor-specific idiotype which can be monitored via peripheral blood flow cytometric analysis). These chimeras showed complete donor chimerism in myeloid, B- and T-lymphocytic lineages by day +100 following transplantation, and splenocytes from these chimeras exhibited tolerance to host-type but not third-party alloantigens. BALB/c hosts were given 800 cGy TBI on day -1, followed on day 0 by intravenous administration of 500 BCL₁ tumor cells and infusion of 0.3x 10⁶ CD8+ T cells of C57 origin (H-2^b+) sorted by flow cytometric analysis from the either spleens of the chimeric mice or from the spleens of untreated wild-type C57BL/6 mice. All hosts were given 5 x 10⁶ T cell-depleted wild-type C57 bone marrow cells. All mice were observed for clinical signs of graft-versus-host disease (GVHD) and mortality through day +100. Autopsy was performed at death to assess for sub-clinical target organ involvement with GVHD or tumor. Donor chimerism and BCL₁ status was assessed at day +28 and day +100 by 3-color flow cytometric analysis for donor-specific MHC versus T-, B- and myeloid lineage markers as well as tumor-specific idiotype in the peripheral blood (or in the spleen at time of death for animals dying prior to day +100).

All animals receiving BCL₁ tumor cells and sorted CD8+T cells from wild-type untreated C57 donors cleared tumor idiotype but succumbed to GVHD. All animals receiving tumor cells and sorted chimeric C57 CD8+ T cells remained free of clinical or pathologic evidence of GVHD, but died with tumor progression. Control myeloablated animals given C57 TCD BM alone with BCL₁ tumor cells all succumbed to tumor, whereas those receiving C57 whole bone marrow with tumor demonstrated tumor survival without GVHD. The data indicate that chimeric donor peripheral CD8+ T cells, which lose their capacity to induce lethal GVHD in BALB/c hosts, also lose the capacity to eradicate BALB/c-type lymphoma cells. We conclude that CD8+ T cell-induced GVT effect in this model is dependent upon alloantigen rather than tumor-specific antigen recognition.