Immunobiology and ImmunotherapyImmunogenicity of murine mPEG-red blood cells and the risk of anti-PEG antibodies in human blood donors

- In vivo survival of murine methoxypoly(ethylene glycol) (mPEG)-red blood cells (RBCs) after repeated transfusions is normal.
- Soluble PEG, before or after mPEG-RBC transfusions, did not induce anti-PEG immunoglobulin (Ig)G.
- Findings in humans do not support reports that 25% of blood donors have anti-PEG IgG.
- The high rate of anti-PEG IgG in earlier reports is due to methodologic false positives.
- Methoxy-PEG-RBCs remain an option for the treatment/prevention of non-ABO alloimmunization.

The immunocamouflage of non-ABO blood group antigens by membrane-grafted methoxypoly(ethylene glycol) (mPEG) may attenuate the risk of red blood cell (RBC) alloimmunization. However, concerns have been raised over the immunogenic risk of PEG and PEG-RBCs. To assess this risk, murine and human studies were performed. Mice were exposed to soluble PEG prior to, or between, multiple transfusions (∼60-day intervals) of control or mPEG-RBCs, and cell survival was determined by flow cytometry. In some studies, the control and mPEG-RBC groups were reversed after one or more transfusions. Furthermore, human blood donors and commercial intravenous immunoglobulin products were examined to detect anti-PEG antibodies and to assess the risk for false positives. Naïve mice receiving chronic mPEG-RBC transfusions had normal RBC survival curves with no evidence of anti-PEG antibodies. Similarly, challenge with soluble PEG did not elicit anti-PEG antibodies in mice. Studies in humans revealed no evidence of a high prevalence of anti-PEG antibodies in either blood donors or commercial intravenous immunoglobulin. However, by use of the methods employed by studies identifying high levels of anti-PEG antibodies, a significant level (∼15%) of “false positives” were detected in commercial antibodies of known (non-PEG) specificities. These findings suggest that methodologic problems yielded a high rate of false positives in these earlier studies. These data continue to support the clinical utility of cellular PEGylation and the low immunogenic risk of grafted mPEG.

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