Soluble CD4-PE40 is cytotoxic for a transfected mammalian cell line stably expressing the envelope protein of human immunodeficiency virus (HIV-1), and cytotoxicity is variably inhibited by the sera of HIV-1-infected patients.
Sera were obtained from 50 individuals infected with human immunodeficiency virus type 1 or from HIV-1-uninfected individuals before or after vaccination with recombinant gp160. These sera were evaluated for activity antagonistic to the cell-killing activity of the chimeric Pseudomonas exotoxin hybrid protein, sCD4-PE40. For these studies, Chinese hamster ovary (CHO) cells were transfected with a chimeric plasmid encoding the tat, rev, and envelope genes of HIV-1 and a cell line was selected for stable expression of the envelope glycoproteins at the cell surface (CHO-env). Cytotoxicity of sCD4-PE40 for CHO-env in the presence or absence of added human serum was quantitated spectrophometrically following enzymatic reduction of a tetrazolium bromide within the mitochondria of viable cells (MTT assay). Several HIV+ sera inhibited the cytotoxic activity of sCD4-PE40; the antagonist had properties consistent with those of immunoglobulins in that it was heat stable, absorbed by protein A, and reversible by increasing the concentration of sCD4-PE40. Of 15 HIV+ sera which strongly reacted with gp120, 11 (73%) also potently inhibited sCD4-PE40 cytotoxicity, and cytotoxicity was inhibited by sera from some HIV- individuals after, but not before, immunization with gp160. These data suggested a role for antibody to gp120 in the antagonistic activity. However, not all sera with antibody to gp120 antagonized sCD4-PE40 cytotoxicity and high levels of antagonist activity were frequently (40%) found in HIV+ sera lacking immunoblot-detectable antibody to gp120, or antibody to either CD4 or PE40. Grouping of the HIV+ sera according to the patients' absolute number of CD4+ cells revealed that the degree of inhibition of sCD4-PE40 cytotoxicity approached a Gaussian distribution, suggesting that persons with CD4+ cell counts between 200 and 700/mm3 may be more likely to possess significant levels of serum antagonist. This data have implications for the clinical development of sCD4-PE40 or other sCD4-based therapeutics in the management of HIV-1 infection.
Pitts
T W
TW
Department of Cancer and Infectious Diseases, Upjohn Laboratories, Kalamazoo, MI 49007.
Bohanon
M J
MJ
Leach
M F
MF
McQuade
T J
TJ
Marschke
C K
CK
Merritt
J A
JA
Wierenga
W
W
Nicholas
J A
JA
D036002:ADP Ribose Transferases; D000818:Animals; D001427:Bacterial Toxins; D015704:CD4 Antigens / Q000276:immunology*; D016466:CHO Cells; D006224:Cricetinae; D003602:Cytotoxicity, Immunologic; D005098:Exotoxins / Q000276:immunology*; D005814:Genes, Viral; D015483:HIV Antibodies / Q000097:blood; D015699:HIV Envelope Protein gp120 / Q000276:immunology; D015658:HIV Infections / Q000276:immunology*; D015497:HIV-1 / Q000235:genetics / Q000276:immunology*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D011994:Recombinant Proteins / Q000276:immunology; D012995:Solubility; D014162:Transfection; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A
D036002:ADP Ribose Transferases; D001427:Bacterial Toxins; D015704:CD4 Antigens; D005098:Exotoxins; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; D011994:Recombinant Proteins; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A