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Previous work has shown failure of engraftment in lethally irradiated dogs when autologous marrow was depleted of Ia-positive cells with an anti-Ia antibody and complement before infusion. In the current study, we have utilized an avidin-biotin immunoadsorption procedure to obtain a population of highly enriched Ia-positive cells for autologous bone marrow transplantation in dogs given lethal irradiation. Dog marrow cells (2.4 to 7.0 X 10(9) cells) that contained 8.6% to 19.9% Ia- positive cells were treated successively with monoclonal antibody 7.2, which reacts with a framework determinant of Ia-antigen, and biotin- conjugated goat antimouse immunoglobulin. These treated cells were passed over a column of avidin-Biogel (polyacrylamide) and the adherent cells removed by mechanical agitation. Seven lethally irradiated dogs were transplanted with 5.9 to 33.4 X 10(6) recovered adherent cells per kilogram of which 69.0% to 88.0% were Ia-positive. All dogs had hematologic recovery; six are alive and well with durable engraftment and one died on day 15 posttransplant. They are immunologically normal as determined by lymph node and bone marrow biopsies, lymphocyte function, and immunophenotyping of peripheral blood and bone marrow cells. These data provide further evidence that canine hematopoietic stem cells express Ia-like antigens and that these cells are capable of complete hematopoietic and immunologic reconstitution in an autologous model.

Biotinylated antibodies and an avidin-Sepharose 6MB column were utilized in a novel approach to deplete selected cell populations from human bone marrow. Fluorescein-labeled Daudi lymphoblasts were mixed with bone marrow mononuclear cells in a model system, and removal of Daudi cells was quantitatively assessed with an inverted fluorescent microscope. Treatment using the biotinylated monoclonal antibody 2H7 reactive with Bp32 antigen (expressed on Daudi cells) followed by passage over avidin-Sepharose produced greater than two logs of Daudi cell removal from bone marrow. An alternative method was tested by treating cells successively with nonbiotinylated monoclonal antibody and biotinylated goat antimouse immunoglobulin followed by passage over avidin-Sepharose. Up to three logs of Daudi cells could be eliminated from bone marrow with quantitative recovery of hematopoietic progenitors. The use of biotinylated goat antimouse immunoglobulin eliminates the need to prepare a biotin conjugate of each individual monoclonal antibody. The clinical application of cellular immunoadsorption using the avidin-biotin system may prove useful in bone marrow transplantation.