The anti-CD2 monoclonal antibody BTI-322 generates unresponsiveness by activation-associated T cell depletion.

The antihuman CD2 MoAb BTI-322 (Lo-CD2a) effectively inhibits T cell responses in vitro to allogeneic cells, which is followed by unresponsiveness to the original stimulator in secondary stimulation. We studied the xenogeneic human antiporcine mixed lymphocyte reaction (MLR), and utilized anti-T cell receptor (TCR) Vbeta family antibody-induced cell proliferation to determine the specificity and mechanism. BTI-322 and its humanized version, MEDI-507, effectively inhibited the primary xenogeneic MLR. After suboptimal primary stimulation using lower numbers of xenogeneic stimulator cells, the unresponsiveness in secondary culture was apparent only for xenogeneic stimulator cells of the original SLA haplotype, and not for third-party stimulators or allogeneic cells. The inhibition of primary MLR was not observed for nylon-wool-purified T cells, but was seen after reconstitution of purified T cells with monocytes. Similarly, anti-Vbeta family-specific stimulation showed family-specific unresponsiveness in secondary culture. This required the presence of the whole BTI-322 molecule: a F(ab')2 fragment was not effective. T cells of a distinct Vbeta family were depleted after stimulation with an anti-Vbeta family-specific antibody and BTI-322. We conclude that the inhibition by BTI-322 of a primary xenogeneic MLR or the response to an anti-TCR Vbeta antibody is associated with unresponsiveness upon restimulation, due to activation-associated cell depletion. In this process, the interaction between monocytes and the Fc part of the antibody is involved. This unique characteristic of BTI-322 suggests the potential of the antibody for tolerance induction in vivo, besides the potential use as a T cell depleting agent.

The recovery of highly purified biopharmaceuticals from perfusion cell culture bioreactors.

The impact of continuous perfusion cell culture technology on production of one and two chain human rtPA, as well as monoclonal IgG and IgM, will be reviewed. Perfusion as compared to batch systems improve the quality of the product in the conditioned media in terms of biological activity and structural integrity. This significantly increases downstream recovery and daily production output of final purified material. These findings are a consequence of the ability of perfusion technology to 1) maintain cells intact at high cell density; 2) effectively reduce serum content to approximate serum free conditions; and 3) minimize residency time of labile product within the 37 degrees C environment of the bioreactor.

Serological characterization of HTLV-III infection in AIDS and related disorders.

Current efforts to test blood donors and other persons for exposure to the human T cell lymphotropic virus type III (HTLV-III), the etiologic agent of the acquired immunodeficiency syndrome (AIDS), are based on the measurement of serum antibodies to viral antigens. We studied presence of serum antibodies to HTLV-III-related antigens from 767 individuals with AIDS or AIDS-related complex (ARC) or asymptomatic persons at risk for AIDS by using ELISA and immunoblot techniques. Of the 280 specimens from AIDS and ARC subjects that were tested, 99% were ELISA reactive and 96% were immunoblot reactive. Greater than 96% of the seropositive subjects manifested antibodies to the p24 core antigen, whereas only 88% had antibodies to the gp41 envelope-related glycoprotein. Contrary to previous reports, a short incubation time in the immunoblot assay failed to detect low-titer or low-affinity antibodies that were detected by overnight incubation. There was no apparent difference in pattern of antibodies to HTLV-III-related antigens in symptomatic vs. asymptomatic seropositive individuals.