Minor antigen distribution predicts site-specific graft-versus-tumor activity of adoptively transferred, minor antigen-specific CD8 T Cells

Abstract

The clinical success of allogeneic T cell therapy for cancer relies on the selection of antigens that can effectively elicit antitumor responses with minimal toxicity toward nonmalignant tissues. Although minor histocompatibility antigens (MiHA) represent promising targets, broad expression of these antigens has been associated with poor responses and T cell dysfunction that may not be prevented by targeting MiHA with limited expression. In this study, we hypothesized that antitumor activity of MiHA-specific CD8 T cells after allogeneic bone marrow transplantation (BMT) is determined by the distribution of antigen relative to the site of tumor growth. To test this hypothesis, we utilized the clinically relevant male-specific antigen HY and studied the fate of adoptively transferred, HY-CD8(+) T cells (HY-CD8) against a HY-expressing epithelial tumor (MB49) and pre-B cell leukemia (HY-E2APBX ALL) in BMT recipients. Transplants were designed to produce broad HY expression in nonhematopoietic tissues (female → male BMT, [F → M]), restricted HY expression in hematopoietic tissues (male → female BMT, [M → F]) tissues, and no HY tissue expression (female → female BMT, [F → F]). Broad HY expression induced poor responses to MB49 despite sublethal graft-versus-host disease and accumulation of HY-CD8 in secondary lymphoid tissues. Antileukemia responses, however, were preserved. In contrast, restriction of HY expression to hematopoietic tissues restored MB49 responses but resulted in a loss of antileukemia responses. We concluded that target alloantigen expression in the same compartment of tumor growth impairs CD8 responses to both solid and hematologic tumors.

Keywords: Acute lymphoblastic leukemia; Adoptive T cell therapy; Allogeneic transplantation; CD8 T cell function; Minor histocompatibility antigens.

Figure 1. Adoptively transferred HY-specific CD8 T-cells expand and produce GVHD in allogeneic males

Lethally irradiated B6 male mice received 5×10⁶ T-cell (CD3) depleted marrow on Day 0, followed by 1×10⁷ HY-specific CD8 by tail vein injection on Day +7. Clinical GVHD scoring was performed once weekly. (A) Composite GVHD scores on Day +60 posttransplant were consistent with sublethal GVHD, particularly manifested as (B) changes in skin integrity, fur ruffling and posture/activity, compared with no clinical signs of GVHD in syngeneic female recipients of female BMT. GVHD scoring data represent 4 independent experiments with 6–10 mice/group. (C) HY-specific CD8 were enumerated from spleen and bone marrow of transplant recipients by flow cytometry 7 and 28 days after adoptive transfer (Day +14 and +35 post-BMT) by gating on live, CD8a+CD45.2+ cells. Representative flow plots (left panel) and total numbers of CD8a+CD45.2+ cells per 100,000 splenocytes (right panel, top) or bone marrow cells (left panel, bottom) are shown.

Figure 2. Adoptively transferred HY-specific CD8 cannot control MB49 in male recipients

Experimental [F→M] and control [F→F] B6 mice received T-cell depleted B6 female bone marrow on Day 0, followed by adoptive transfer of HY-CD8 on Day +7. They were then challenged with 1×10⁵ MB49, an HY-expressing epithelial tumor, subcutaneously on Day +14. Tumor-free survival was followed daily (A), and tumor volumes measured in 2 dimensions twice weekly (B). [F→M] recipients (closed square, solid line) had poor tumor control, similar to [F→F] controls that did not receive HY-CD8 (dotted line, closed triangle). [F→F] recipients of HY-CD8 preserved immune responses. Enumeration of adoptively transferred HY-CD8 in spleen as live, CD8a+CD45.2+ cells 14 days after adoptive transfer showed significant accumulation of HY-CD8 in [F→M] despite poor tumor control, compared to [F→F] tumor bearing (closed circle) or tumor-free recipients. (D) Expression of PD-1 (gray shaded) compared to IgG2k isotype controls (black dotted) was measured on live, CD8⁺CD45.2⁺ HY-specific CD8 on Day +14 post BMT (at the time of MB49 injection) by flow cytometry. Expansion data and PD-1 histograms are representative of at least 4 independent experiments with 6–10 mice/group. (E) Live, CD8⁺CD45.2⁺ cells were collected by flow sorting on Day +14 post-BMT and restimulated in vitro with the Class I immunodominant HY peptide (UTY). Proliferation was measured by CFSE dilution at 72 hours. Naïve female MataHari (HY-specific) splenocytes served as controls.

Figure 3. HY-expressing dendritic cell vaccination cannot restore antitumor responses in [F→M] recipients of HY-specific CD8 who express HY in nonhematopoietic tissues

Lethally irradiated female or male B6 recipients were transplanted with TCD female B6 BM on Day 0, 1×10⁷ HY-CD8 on Day +7 and 1×10⁵ CD40-activated male dendritic cells were injected intraperitoneally also on Day +7.. AlloHSCT recipients were then followed for (A) tumor-free survival and (B) tumor growth in [F→F] recipients (closed triangle, solid line) and [F→M] recipients (closed square, solid line), with rapidly growing tumors (closed square, solid line). Unvaccinated [F>M] (closed square, dotted line) and [M>F] (closed triangle, dotted line) who received HY-CD8 served as controls. Survival and tumor volume curves are representative of 3 independent experiments with 8–10 mice/group.

Figure 4. Hematopoietic restriction of HY preserves responses to MB49 despite PD1 expression on adoptively transferred HY-specific CD8

To restrict HY to hematopoietic tissues, lethally irradiated female B6 mice received T-cell depleted B6 male [M→F] BMT on Day 0 followed by 1×10⁷ HY-specific CD8 on Day +7. AlloHSCT recipients were (A) clinically graded for GVHD and total bone marrow cells recorded after erythrocyte lysis to assess overall marrow cellularity. (B) Recipients were next challenged with MB49 on Day +14 and followed for tumor-free survival in [F→M] (closed square) and [M→F] (closed diamond) groups. Data shows a single experiment representative of 3 independent experiments with 8–12 mice/group. (C) Accumulation of HY-CD8 was measured by flow cytometry as live, CD8a+CD45.2+ cells 14 days after adoptive transfer via representative contour plots (left panels) and absolute numbers per 100,000 splenocytes (right, top panel) or bone marrow cells (right, bottom panel). (D) PD-1 expression was measured by flow cytometry on HY-CD8 in the spleen and bone marrow of [M→F] and [F→M] recipients 14 days after adoptive transfer. Histograms depict live, CD8a⁺CD45.2⁺PD1⁺ cells (gray shaded) compared to IgG2k isotype controls (dashed line). Data shown are representative of 3 independent experiments. (E) To verify functionality, HY-CD8 were sorted from [F→M] and [M→F] ex vivo 14 days after adoptive transfer, restimulated with UTY peptide, and proliferation measured by CFSE dilution after 72 hours. (F) Expression of PDL-1 (B7:H1), the ligand for PD-1, was measured by flow cytometry in MB49 prior to subcutaneous injection (gray shaded) and at Day +28 in animals that succumbed to tumor-related mortality and shown in this representative histogram.

Figure 5. Hematopoietic restriction of HY does not preserve antileukemia responses, which are restored with broad expression of HY

(A) Immunogenicity of a murine, male, GFP-conjugated pre-B cell ALL (E2APBX-ALL) was determined by coculturing 1×106 male vs female E2APBX with 1×10e6 MataHari splenocytes and measuring interferon gamma production by ELISA at 48 hours. Male dendritic cells and naïve MataHari splenocytes alone served as positive and negative controls, respectively. (B) Overall survival was measured after 1×10⁵ E2APBX-ALL cells were incorporated into T-cell depleted intravenous grafts into ([F—M] solid square), ([M→F], solid diamond) and ([F→F], solid circle) recipients on Day 0, followed by adoptive transfer of HY-CD8 on Day +7. [F→F] who did not receive HY-CD8 (dotted line) served as negative controls. (C), The quantity of GFP+ cells in the bone marrow was assessed by flow cytometry to measure leukemia burden either at time of death or Day+72 posttransplant. (D) Number of bone marrow-infiltrating HY-CD8 (live, CD8+CD45.2+) on Day +7, +14 and +21 following T-cell depleted transplant and coinjection (intravenously) of 1×10⁵ E2APBX-ALL cells. Data shown are representative of 3 independent experiments.

Figure 6. Expression of PDL-1 on leukemia cells, but not PD-1 on HY-CD8, correlates with improved leukemia control when HY is broadly expressed

(A). The percent of HY-specific CD8 (live, CD8+CD45.2) that were also PD1+ was measured by flow cytometry at Day +7, +14 and +21 following T-cell depleted transplant into [F>M], [M>F] and [F>F] recipients who simultaneously received 1×10⁵ E2APBX-ALL cells on Day 0. PD-1 and Tim-3 expression (gray shaded) compared to IgG2k isotype controls was measure on live, CD8⁺CD45.2⁺ cells from the bone marrow was measured by flow cytometry at either study endpoint or at the time of death (left panels). Data shown are representative of 2 independent experiments. (B) Percentage of total GFP+B220+ E2APBX-ALL expressing PDL1 (right panels) was measured by flow cytometry on Day +7, +14 and +21 post-transplant and leukemia challenge (center panels). Representative histograms comparing PDL-1 fluorescence intensity on Day +7 (dotted lines) and +14 (solid lines) are also shown. A contour plots showing the gating strategy for identification of live, B220+GFP+ HY-E2APBX-ALL in the bone marrow is shown to the far right. Data shown are representative of 2 independent experiments.