Comparative analysis of polymer and linker chemistries on the efficacy of immunocamouflage of murine leukocytes.

Membrane grafting of methoxypoly(ethylene glycol) [mPEG] to allogeneic leukocytes attenuates allorecognition and significantly reduces the risk of graft-versus-host disease in mice. To optimize the immunological efficacy of polymer grafting, murine splenocytes were modified using three differing linker chemistries: CmPEG (5 kDa), BTCmPEG (5 and 20 kDa) and TmPEG (5 kDa). In vitro immunocamouflage efficacy was examined by flow cytometic analysis of leukocyte markers and mixed lymphocyte reactions (MLR). In contrast to CmPEG and BTCmPEG, TmPEG exerted significant cellular toxicity. Flow cytometric analysis demonstrated that both CmPEG and BTCmPEG were highly effective at camouflaging cell surface markers while TmPEG was ineffective. Furthermore, CmPEG and BTCmPEG dramatically blocked MLR allorecognition and cellular proliferation. Polymer length was the most critical factor in the immunocamouflage of cells with the BTCmPEG 20 kDa being the most effective. In contrast to other immunomodulatory approaches, immunocamouflage of leukocytes yields a multivalent effect globally interfering with attachment, allorecognition, presentation and costimulation pathways.