Metabolic Regulation of Alloimmunity: Inhibition of PKM2 Attenuates T Cell Activation and Prolongs Allograft Survival

Introduction/Rationale: Organ transplantation is a life-saving therapy, but its success is limited by immune rejection and the toxicity of immunosuppressants. Activation of immune cells depends on metabolic reprogramming, particularly a shift from mitochondrial respiration to aerobic glycolysis (Warburg effect). Pyruvate kinase M2 (PKM2), a glycolytic enzyme upregulated during immune activation, links metabolism to pro-inflammatory gene expression. Although implicated in cancer and autoimmunity, the role of PKM2 in transplant rejection remains unclear. We hypothesized that PKM2 supports alloimmune T-cell responses and that its inhibition could mitigate rejection and improve graft outcomes

Methods: To assess PKM2 expression during rejection, C57BL/6 (B6) mice received heart grafts from syngeneic B6 or fully mismatched BALB/c (B/c) donors. Heart grafts were harvested and analyzed by FACS on postoperative days (POD) 3 and 7. For T cell alloresponse, CD3⁺ cells (B/c mice) were treated with PKM2 inhibitors (PKM2i) or vehicle and co-cultured with allogeneic BMDCs (B6 mice). To assess graft survival and immune mechanisms in vivo, heart transplant recipients (B/c → B6) were treated with PKM2i or vehicle (2×/week, i.p.) from POD1–28. Recipient's spleen and heart grafts were harvested on POD14 for ex vivo analyses (FACS+Histology)

Results: PKM2 expression was strongly upregulated in graft-infiltrating immune cells, peaking in T cells by POD7, while syngeneic grafts remained at baseline. Strikingly, PKM2 inhibition significantly extended graft survival and broadly suppressed T-cell alloimmune responses including reduced T-cell infiltration, lower IFN-γ production (in vitro/in vivo), and decreased expression of activation/proliferation markers (CD25, Ki67). These changes were accompanied by clear histologic evidence of reduced immune-mediated tissue injury.

Conclusion: These findings position PKM2 as a central regulator of T-cell–mediated rejection and a promising therapeutic target for metabolic immune modulation in transplantation.