Anti-CD34(+) fabs generated against hematopoietic stem cells in HIV-derived combinatorial immunoglobulin library suggest antigen-selected autoantibodies

Bone marrow suppression associated with HIV infection does not appear to be solely due to direct viral cytopathic effects. Autoantibodies may play a r ole in myelosuppression, however it is unclear whether autoantibodies produ ced in HIV infection represent a primary pathogenic process or merely refle ct polyclonal B cell activation. To address these questions, we generated c ombinatorial immunoglobulin libraries using the pComb3 phagemid from an HIV + individual with evidence of circulating autoantibodies. From one library, three anti-CD34 Fabs were identified using fresh CD34(+) cells as antigeni c targets by a method of phage subtraction. The anti-CD34 Fabs are specific by immunoblotting and Elisa and are of high affinity, with calculated Kds in the range of 10(-7)-10(-8) M. Nucleic acid sequencing revealed all three to be of the VH3 family and to have lambda light chains with some gene seg ments expressing little somatic mutation, while other segments were somatic ally mutated in patterns suggestive of antigen selection. These findings in dicate that(1) A subset of HIV-associated anti-CD34 autoantibodies are mono specific and antigen-selected and are not merely a consequence of polyclona l B cell activation and elevated Ig levels in HIV. Autoreactivity in HIV th erefore includes both polyspecific, low affinity antibodies as well as mono specific antigen-selected high affinity antibodies. (2) Although bone marro w suppression in HIV is likely to be multifactorial, autoantibodies to hema topoietic stem cells may contribute to its pathogenesis. (3) Library sampli ng of VH gene family rearrangements shows no evidence for under-representat ion of the VH3 family in the immune dysregulation of HIV infection. Phage s ubtraction is corroborated to be an effective means of identifying, cloning , and characterizing antibodies to hematopoietic differentiation antigens. (C) 1998 Elsevier Science Ltd. All rights reserved.