Analytical variables of reverse transcription-polymerase chain reaction-based detection of disseminated prostate cancer cells.

Early systemic spread of occult tumor cells that may develop into founders of incurable distant metastasis has been identified in prostate cancer patients by reverse transcription-PCR (RT-PCR) amplification of prostate-specific antigen (PSA) mRNA. Nevertheless, the introduction of this new staging tool into the clinical setting has been hampered by the disparate and contradictory data on the sensitivity and specificity of RT-PCR methods reported recently. We used PSA RT-PCR to examine the influence of analytical variables such as priming and enzyme of reverse transcriptase reaction, temperature and time of primer annealing, primer extension and denaturation, as well as the concentrations of magnesium chloride, Taq polymerase, deoxynucleotide triphosphate, primers and BSA on the amplification process. By systematically varying these chemical and physical components, we could demonstrate a significant increase in amplification yield and in stringency of primer annealing. This may explain the wide variety of published findings on molecular staging of prostate cancer, which currently impedes the clinical introduction of PSA RT-PCR assays in prostate cancer. Methodological analyses are needed for standardization and quality assurance to achieve reproducible molecular methods that can be used in clinical practice.

Minimal costimulatory requirements for T cell priming and TH1 differentiation: activation of naive human T lymphocytes by tumor cells armed with bifunctional antibody constructs.

Direct priming of naive human CD8+ and CD4+ T cells by tumor cells devoid of any intrinsic antigen presentation properties, but passively armed with recombinant proteins mediating primary and costimulatory T cell signals, was investigated. Bifunctional antibody constructs were used to specifically target costimulatory molecules such as B7-1, B7-2 and LFA-3 to the epithelial cell adhesion molecule (EpCAM), a surface antigen successfully used as target for antibody therapy of minimal residual colorectal cancer. T cell priming was monitored by flow cytometric analysis of CD45 isoform expression and confirmed by measuring typical effector functions of primed T cells known to be absent from naive T lymphocytes. Accordingly, CD8+ T cells were tested for cytotoxic activity and secretion of TNF-alpha, while secretion of IFN-gamma, IL-5 and IL-4 was determined for CD4+ T cells. B7, known to be required for the initial activation of naive T cells, also proved to be sufficient for T cell priming when present as the only costimulatory molecule together with an appropriate primary signal. The requirement of dendritic and other antigen presenting cells (APCs) for T cell priming through non-APCs such as tumor cells could be ruled out. Under minimal priming conditions, naive CD4+ T cells were found to exclusively enter the TH1 developmental pathway, while several factors thought to favor TH2 polarization, like weak primary signals and B7-2 versus B7-1 costimulation, could be excluded as dominant TH2 promoters.

Construction and biological activity of a recombinant bispecific single-chain antibody designed for therapy of minimal residual colorectal cancer.

Unlike monoclonal antibodies, clinical application of bispecific antibodies has so far lagged behind because of difficult, low-yield production techniques as well as considerable toxicity attributed to bispecific antibody preparations containing immunoglobulin-Fc parts and anti-CD3 homodimers. These difficulties were overcome by recombinant generation of a bispecific single-chain antibody (bscAb) joining two single-chain Fv fragments via a five-amino-acid glycine-serine linker. The anti-CD3 specificity directed against human T cells was combined with another specificity against the epithelial 17-1A antigen. The following domain arrangement was critical in this individual case to obtain a fully functional bscAb: VL17-1A-VH17-1A-VHCD3-VLCD3. The bscAb was expressed in chinese hamster ovary cells with a yield of 15 mg/l culture supernatant whereas numerous attempts to obtain a functional protein expression in Escherichia coli failed. The low-molecular-mass bispecific construct (60 kDa) could easily be purified by its C-terminal histidine tail. The antigen-binding properties are indistinguishable from those of the corresponding univalent single-chain Fv fragments as shown by enzyme immunoassay and flow cytometry. We could show that the bscAb, which lacks Fc parts and anti-CD3 homodimers is highly cytotoxic for 17-1A positive tumor cells in nanomolar concentrations and in the presence of human T cells. Most remarkable, it does not stimulate T lymphocyte proliferation in the absence of tumor cells and, moreover, does not induce CD25 up-regulation and the secretion of potentially toxic lymphokines such as tumor necrosis factor alpha, interleukin-6 and interferon gamma. Maximal cytotoxicity (51Cr release) was achieved without notable costimulation and was not further enhanced by adding costimulatory signals such as those delivered by anti-CD28 antibodies. CD8+ as well as CD4+ T cell subpopulations were recruited to exert cytotoxicity against tumor cells with different kinetics. CD8+ cells induced high 51Cr release within 4 h while CD4+ cells required a 20-h incubation. The systemic application of the 17-1A/CD3-bscAb could be a major improvement in therapy against disseminated micrometastatic tumor cells. A prospective, randomized clinical trial showing that an anti-17-1A monoclonal antibody could prolong survival of colorectal cancer patients after 5 and 7 years, warrants an assessment of the clinical efficacy of this bscAb exhibiting a 1000-fold higher specific cytotoxicity against tumor cells in vitro.

A recombinant bispecific single-chain antibody, CD19 x CD3, induces rapid and high lymphoma-directed cytotoxicity by unstimulated T lymphocytes.

Although bispecific antibodies directed against malignant lymphoma have been shown to be effective in vitro and in vivo, extended clinical trials so far have been hampered by the fact that conventional approaches to produce these antibodies suffer from low yields, ill-defined byproducts, or laborious purification procedures. To overcome this problem, we have generated a small, recombinant, lymphoma-directed, bispecific single-chain (bsc) antibody according to a novel technique recently described. The antibody consists of 2 different single-chain Fv fragments joined by a glycine-serine linker. One specificity is directed against the CD3 antigen of human T cells, and the other antigen-binding site engages the pan-B-cell marker CD19, uniformly expressed on the vast majority of B-cell malignancies. The construct was expressed in Chinese hamster ovary cells and purified by its C-terminal histioline tag. Specific binding to CD19 and CD3 was demonstrated by fluorescence-activated cell sorter analysis. By redirecting unstimulated primary human T cells derived from the peripheral blood against CD19-positive lymphoma cells, the bscCD19 x CD3 antibody showed significant cytotoxic activity at very low concentrations of 10 to 100 pg/mL and at effector to target cell ratios as low as 2:1. Moreover, strong lymphoma-directed cytotoxicity at low antibody concentrations was rapidly induced during 4 hours even in experiments without any T-cell prestimulation. Thus, this particular antibody proves to be much more efficacious than the bispecific antibodies described until now. Therefore, the described bscCD19 x CD3 molecule should be a suitable candidate to prove the therapeutic benefit of bispecific antibodies in the treatment of non-Hodgkin lymphoma. (Blood. 2000;95:2098-2103)