Acquired microRNA (miR)-142 Deficit Drives Immune Escape in Acute Myeloid Leukemia (AML)

Loss of function of T cells has been associated with AML growth and poor outcomes. MiR-142 reportedly regulates normal hematopoiesis. Loss of the mir142 gene in the mouse results in decreased hematopoietic output and reduced T and NK cells. Mutated MIR142 was found in AML patients (pts). Recently, while we observed that miR-142-3p levels were lower in blasts and associated with shorter survival (p=0.0288) in AML pts vs. healthy donors, we found that in these pts, T cells were also fewer, with reduced miR-142 levels, increased levels of PD-1 (a marker for activation/exhaustion) and reduced cytokine production, supporting impaired T cell immune activity. Similarly, in Mll^PTD/WTFlt3^ITDITD mice, a murine AML model, T cells were also decreased, and had reduced miR-142 levels, increased spontaneous apoptosis and PD-1 expression, and reduced proliferation rate and cytokine production, compared to T cells from normal wild-type (wt) mice. Since we have shown that miR-142 deficit impairs T cell antileukemic activity in chronic myeloid leukemia (CML; ASH 2023, Abstract #3152), we hypothesize that during AML growth, T cells acquire a miR-142 deficit that contributes to immune escape and disease progression.

To test this hypothesis, first we co-transplanted Mll^PTD/WTFlt3^ITDITD AML leukemic stem cells (LSC, i.e., Lin-Sca-1+c-Kit+, LSKs) with Mir142^+/+ T or Mir142^−/− T cells into immunodeficient NSG recipients, which lack T cells. We observed significantly decreased T cell engraftment, increased leukemic blasts, and shorter survival in LSK+Mir142^−/− T recipients compared with LSK+Mir142^+/+ T recipients (median: 51 vs 59 days, p=0.0013). Second, we transplanted AML LSKs into Mir142^−/− or Mir142^+/+ recipients and observed significantly higher leukemic burden and shorter survival in Mir142^−/− than in Mir142^+/+ recipients (median: 32 vs 44 days, p<0.0001). Third, we transplanted AML LSKs into Mir142^flox(f)/fLck-cre+ (i.e., miR-142 KO in T cells only) or cre- mice and monitored these mice for survival (ongoing). Fourth, we co-transplanted human AML blasts with miR-142 KD or wt T cells into NSGS mice. The AML+KD-T recipients have a higher leukemia burden and shorter survival than the AML+wt-T recipients (median: 32 vs 41 days, p=0.0017). Collectively, these results suggest that miR-142 deficit in T cells mediates T cell dysfunction and promotes LSC growth and disease progression.

To determine how T cells acquire miR-142 deficit during AML growth, we co-cultured murine T cells with BM cells from Mll^PTD/WTFlt3^ITDITD AML or normal wt mice in a transwell and observed lower miR-142 levels and increased PD-1 in T cells co-cultured with AML blasts (p<0.05 for both). Next, we transplanted BM cells from AML or normal wt mice into congenic wt recipients and observed lower miR-142 and increased PD-1 levels in the host T cells from the recipients of AML blasts (p<0.05 for both). This data suggested a possible role of blast-secreted cytokines in the induction of T-cell miR-142 deficit. To this end, we discovered that higher levels of IL-6 in AML were associated with lower T cell levels of miR-142. To determine if increased PD-1 on host T cells contributes to miR-142 deficit-induced T cell exhaustion, we also transplanted AML blasts into PD-1^−/− or wt recipients. We observed significantly longer survival in PD-1^−/− vs. wt recipients (median: 47 vs 36.5 days, p=0.0027).

Next, to test if restoring miR-142 improves T cell control of leukemia growth, we treated a cohort of Mll^PTD/WTFlt3^ITDITD AML mice with M-miR-142 (a synthetic miR-142) or scrambled control (SCR) for 3 weeks. M-miR-142-treated mice had lower disease burden and longer survival (median: 43 vs 38 days, p=0.0006). Recipients of BM from M-miR-142-treated donors also live longer (median: 35 vs 28 days, p<0.0001), supporting reduced LSC burden. Next, AML patient-derived xenograft (PDX) mice were given 10⁶ autologous human T cells and treated with M-miR-142 or SCR for 3 weeks. T+M-miR-142-treated mice had reduced leukemic burden and prolonged survival (median: 60 vs 51 days, p=0.0002) compared with T+SCR-treated controls. Recipients of M-miR-142-treated donor BM also lived significantly longer than recipients of SCR-treated donor BM (median: 92 vs 21 days, p<0.0001).

We concluded that T-miR-142 deficit is acquired during AML progression, causing decreased antileukemic surveillance and contributing to disease growth, which can be rescued by M-miR-142.