Efficacy of anti-CD5 F(ab')2 and Fab' immunoconjugates in human peripheral blood lymphocyte-reconstituted severe combined immunodeficient mice.
A human peripheral blood lymphocyte-reconstituted severe combined immunodeficient (hu-PBL-SCID) mouse model was used to compare in vivo efficacy of immunoconjugates directed against the CD5 antigen present on human T-cells. Four anti-CD5 immunoconjugates were tested, composed of chimeric human-mouse (cH65) F(ab')2 or Fab' fragments chemically linked to recombinant gelonin (rGEL) or the 30,000 M(r) glycoform of ricin A chain (RTA30). Immunoconjugate treatment was initiated approximately 3 weeks after PBL transplantation and consisted of five consecutive daily bolus i.v. injections. Efficacy was subsequently assessed by quantitation of human T-cells in spleens, blood and peritoneal lavage fluid using 3-color flow cytometry. cH65 F(ab')2- and cH65 Fab'-rGEL conjugates were essentially equally effective at depleting human T-cells from SCID mouse tissues, suggesting that bivalent binding is not required for efficacy when rGEL is the cytotoxic moiety. Treatment with unconjugated F(ab')2, unconjugated Fab' or a Fab-rGEL immunoconjugate of irrelevant binding specificity did not result in a significant depletion of T-cells, demonstrating that the cytotoxic moiety and a relevant human T-cell binding moiety are both required for efficacy. In contrast to the results observed with the rGEL conjugates, cH65 Fab'-RTA30 was not as effective as cH65 F(ab')2-RTA30 in depleting human T-cells from SCID mouse tissues. This paralleled in vitro findings in a human PBMC cytotoxicity assay, which demonstrated that cH65 Fab'-RTA30 was 17-fold less potent than cH65 F(ab')2-RTA30 and approximately 50-fold less potent than the rGEL conjugates.(ABSTRACT TRUNCATED AT 250 WORDS)
Kohn
F R
FR
Department of Pharmacology and Toxicology, XOMA Corporation, Berkeley, CA 94710.
Fishwild
D M
DM
Bernhard
S L
SL
Better
M
M
Kung
A H
AH
D000818:Animals; D015703:Antigens, CD / Q000276:immunology; D018956:CD5 Antigens; D005434:Flow Cytometry; D006801:Humans; D007140:Immunoglobulin Fab Fragments; D000922:Immunotoxins / Q000494:pharmacology*; D017708:Leukocyte Transfusion; D051379:Mice; D016513:Mice, SCID; D010529:Peritoneal Cavity / Q000166:cytology; D010835:Phytohemagglutinins / Q000494:pharmacology; D010940:Plant Proteins; D015375:Receptors, Interleukin-2 / Q000187:drug effects; D054789:Ribosome Inactivating Proteins, Type 1; D012276:Ricin; D013154:Spleen / Q000166:cytology; D013601:T-Lymphocytes / Q000187:drug effects
D015703:Antigens, CD; D018956:CD5 Antigens; D007140:Immunoglobulin Fab Fragments; D000922:Immunotoxins; D010835:Phytohemagglutinins; D010940:Plant Proteins; D015375:Receptors, Interleukin-2; D054789:Ribosome Inactivating Proteins, Type 1; C025674:GEL protein, Gelonium multiflorum; D012276:Ricin