CD8+ but not CD4+ T cells require cognate interactions with target tissues to mediate GVHD across only minor H antigens, whereas both CD4+ and CD8+ T cells require direct leukemic contact to mediate GVL

Abstract

Whether T-cell antigen receptors (TCR) on donor T cells require direct interactions with major histocompatibility complex class I or class II (MHCI/MHCII) molecules on target cells to mediate graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) is a fundamental question in allogeneic stem-cell transplantation (alloSCT). In MHC-mismatched mouse models, these contacts were not required for GVHD. However, this conclusion may not apply to MHC-matched, multiple minor histocompatibility antigen-mismatched alloSCT, the most common type performed clinically. To address this, we used wild-type (wt)-->MHCI-/- or wt-->MHCII-/- bone marrow chimeras as recipients in GVHD experiments. For GVL experiments, we used MHCI-/- or MHCII-/- chronic-phase CML cells created by expressing the BCR-ABL cDNA in bone marrow from MHCI-/- or MHCII-/- mice. TCR/MHCI contact was obligatory for both CD8-mediated GVHD and GVL. In contrast, CD4 cells induced GVHD in wt-->MHCII-/- chimeras, whereas MHCII-/- mCP-CML was GVL-resistant. Donor CD4 cells infiltrated affected skin and bowel in wt-->MHCII-/- recipients, indicating that they mediated GVHD by acting locally. Thus, CD4 cells use distinct effector mechanisms in GVHD and GVL: direct cytolytic action is required for GVL but not for GVHD. If these noncytolytic pathways can be inhibited, then GVHD might be ameliorated while preserving GVL.

Figure 1

Experimental design. (A) To create mice with MHCI⁻ or MHCII⁻ parenchyma but with MHC⁺ hematopoietic cells (including APCs), B6 β2M^−/− or IA^bβ^−/− mice (both CD45.2) were irradiated and reconstituted with TCD wt B6 CD45.1 BM. (B) After 3 months to allow for engraftment of the wt B6 hematopoietic system, these chimeras were used as recipients in a second, GVHD-inducing alloBMT.

Figure 2

Dendritic cells in B6 CD45.1→B6 β2M^−/− or B6 IA^bβ^−/− are mostly donor in origin. Spleens and LNs were collagenase-treated, and cells were stained with a cocktail of lineage antibodies, anti-CD11c and anti-CD45.1 or CD45.2 (“Analysis of dendritic cell engraftment”). Shown is CD45.1 (——) and CD45.2 (----) staining of lineage^low CD11c⁺ cells from representative mice (at least 3 mice were analyzed from each group in each experimental repetition).

Figure 3

Wt→β2M^−/− chimeric recipients are resistant to CD8-mediated GVHD. Shown is percentage weight change versus day after alloBMT from 2 independent experiments. Numbers of mice per group in each repetition are listed (separated by commas; *P < .05, CD8 recipients vs recipients of only TCD C3H.SW BM). Weight change was not significantly different at any time point comparing wt→β2M^−/− recipients of only C3H.SW TCD BM and TCD BM plus CD8 cells.

Figure 4

Only wt→wt and not wt→β2M^−/− chimeric recipients of C3H.SW CD8 cells develop histologic GVHD. (A) Representative histology (original magnification ×200). (B) Combined histology scores from 2 independent experiments. Each symbol is the score from an individual mouse; horizontal lines represent mean scores. P values are shown below the group labels.

Figure 5

Both wtgwt and wt→IA^bβ^−/− donor CD4 recipients developed GVHD-induced weight loss. Shown is percentage weight change versus day after BMT from 3 independent experiments. Numbers of mice per group in each repetition are listed, separated by commas (*P < .05, CD4 recipients [either wt→wt or wt→IA^bβ^−/−] vs the appropriate recipients of only TCD 129 BM).

Figure 6

Both wt→wt and wt→IA^bβ^−/− CD4 recipients develop histologic GVHD. (A) Representative histology (original magnification ×200). (B) Combined histology scores from 3 independent experiments. Each symbol is the score from an individual mouse; horizontal lines represent mean scores. P values are shown below the group labels. (C) Immunofluorescent staining of small intestine and skin from both wt→wt and wt→IA^bβ^−/− recipients of 129 CD4⁺ T cells. Blue indicates DAPI-stained nuclei; green, CD4⁺ cells; red, MHCII⁺ cells. Note infiltrating CD4⁺ cells in both bowel and skin of CD4 recipients, frequently adjacent to MHCII⁺ cells.

Figure 7

β2M^−/− and IA^bβ^−/− mCP-CML are resistant to CD8- and CD4-mediated GVL. (A) B6 mice were irradiated and reconstituted with TCD C3H.SW BM, wt B6 or β2M^−/− mCP-CML, with or without C3H.SW donor CD8⁺ T cells. (B) B6 mice were irradiated and reconstituted with TCD 129 BM, wt B6 or IA^bβ^−/− mCP-CML, with or without purified 129 CD4⁺ T cells. (C) To determine whether the GVL resistance of IA^bβ^−/− mCP-CML is in the effector phase, irradiated B6 mice were reconstituted with TCD C3H.SW BM, wt mCP-CML, or IA^bβ^−/− mCP-CML or a mix of both wt and IA^bβ^−/− mCP-CML, with or without purified C3H.SW CD4⁺ T cells. Note that the only survivors were recipients of wt mCP-CML cells and donor C3H.SW CD4 cells, indicating that IA^bβ^−/− mCP-CML is GVL-resistant because of a defect in the effector phase. (D) Experimental design for panel C.