Galpin/DA/N2 IIIBenv 
i.e., they neutralize only the homologous HIV-1 viral strain 60 . This serological 
approach to virus typing has suggested the existence of several major classes of 
HIV-1 strains in North America and further major divergence worldwide 60 . 
However, CTL crossreactivity on the various HIV-1 prototypic strains and clinical 
isolates has not been extensively evaluated. Therefore, the demonstration of CTL 
crossreactivity on cells infected with different HIV-1 isolates may indicate the 
importance of CTL immune responses in treating patients infected with diverse 
clinical HIV-1 strains. 
Ideally, CTL activity should be evaluated on HIV-1 infected target cells. 
However, mouse cells do not have the appropriate cell surface receptor (i.e., CD4) 
for HIV-1 infection, and HIV-1 infected human cells do not possess the appropriate 
MHC restriction elements necessary for mouse CTL recognition. Therefore, an in 
vitro target cell system combining the elements of susceptibility to HIV-1 infection 
and a mouse MHC molecule has been established to facilitate the analysis of CTL 
activity on targets infected with different HIV strains. 
The Hela-T4 cervical carcinoma cell line 61 can be productively infected 
with different HIV-1 isolates, as demonstrated by p24 antigen detection, syncytium 
formation, and cytopathic effects. This cell line has been engineered to express the 
mouse H-2D d MHC molecule and is called Hu/D d . The Hu/D d cell line expresses 
the appropriate MHC restriction element (i.e. H-2D d ) required for mouse CTL 
recognition. Using this target cell system, HIV-1 env-specific mouse CTL should 
be able to recognize and lyse HIV-1 infected human Hu/D d cells because the target 
cells can present HIV- 1 antigens in the context of the mouse class I MHC molecule. 
This genetically engineered target cell system can facilitate the in vitro CTL 
60 LaRosa, G.J., et al„ Science, 249:932-935 (1990). 
6 Madden, et al„ Cell, 47:333-348 (1986). 
Recombinant DNA Research, Volume 17 
