Frederick L. Moolten

Selective Destruction of Target Cells by Diphtheria Toxin Conjugated to Antibody Directed against Antigens on the Cells

Monkey-kidney cells bearing new surface antigens induced by infection with mumps virus were lysed selectively by diphtheria toxin conjugated to antibody against mumps antigens.

An alternative to the magic bullet paradigm for specific cancer therapy

To improve on current cancer therapies, which attack cells on the basis of their proliferative tendencies, much effort has been devoted to a search for properties of tumor cells that are tumor-specific rather than proliferation specific. Evidence from molecular genetic studies suggests, however, that most tumors may lack such properties. An alternative approach to therapy is described that is based on a property known to characterize the majority of human tumors; viz., a monoclonal origin. The strategy requires the prophylactic induction in tissues of mosaicism for genes dictating sensitivity or resistance to chemotherapeutic agents, and exploits the observation that any clone of cells arising in a mosaic tissue must inevitably differ from some other cells in the mosaic. Recent advances in genetic technology imply that the strategy is likely to be testable soon in animals, and that it may significantly improve the results of cancer therapy when a technology safe and efficient enough for its human implementation becomes available.

Formation of adherent monolayers of murine lymphocytes in vitro: The use of serum-free medium and concanavalin a-coated surfaces to promote adherence☆

Murine thymus and spleen cells formed adherent monolayers in polystyrene tissue culture flasks when plated in serum-free medium. In the presence of 2% serum, thymus cells adhered poorly, but adherence was greatly enhanced if the flasks had been coated noncovalently with the lectin, concanavalin A. Adherence of leukemic lymphocytes (L1210) required both serum-free medium and concanavalin A-coated flasks; the extent of attachment was proportional to the concentration of the lectin used to coat the flasks at concentrations up to 0.1 mg/ml. Once L1210 cells had attached, they could not be removed by exposure to serum, ethylenediamine tetraacetic acid, trypsin, or alpha-methyl mannoside. Adherent L1210 cells remained capable of metabolism and proliferation during intervals of up to 7 days. The use of adherent monolayers for cytotoxicity assays was demonstrated by an assay for Pseudomonas aeruginosa toxin in EL4 murine leukemia cells.

Genetic mosaicism and the control of cancer

The susceptibility of animal cells to certain lethal agents, including a variety of cytotoxic drugs, is genetically determined; cells which are otherwise identical may therefore differ in terms of which agents are lethal for them. If such genetic diversity existed within a tissue, exposure to any of these lethal agents would not destroy every cell, but only that fraction of the population that was susceptible. In contrast, if a clone of malignant cells arose from any single cell within such a tissue, the entire malignant clone should be susceptible to destruction by whatever agent its progenitor cells was susceptible to. Treatment of a tumor in a host whose tissues displayed such genetic mosaicism might therefore possess the potential for destroying all tumor cells, at the cost of destroying only a fraction of the normal cells. Prophylactic induction of such mosaicism in normal hosts by genetic manipulation represents a potential future strategy for cancer control. Evidence is presented suggesting that women heterozygous for deficiency of the enzyme hypoxanthine-guanine phosphoribosyl-transferase may constitute naturally occurring examples of such exploitable mosaicism.

In vivo efficacy of HAT therapy against transplantable murine myelomas resistant to purine analogs

The therapeutic efficacy of antineoplastic purine analogs can be jeopardized by the emergence of drug-resistant mutant subpopulations of tumor cells. To determine whether such mutant populations might be eradicable in vivo with the type of HAT combination (hypoxanthine + an antifolate + thymidine) known to be selectively cytotoxic to them in vitro, 2 thioguanine-resistant BALB/c murine myeloma lines were transplanted into BALB/c mice to produce tumors capable of progressive growth in the absence of therapy. Treatment of these mice with a modified HAT regimen induced permanent tumor regressions in 37/44 mice; the same treatment was ineffective against tumors produced by a non-mutant myeloma line from which one of the mutant sublines had been derived.

Rabbits as a Source of Antisera Against SV40 Virus-Induced Cell Surface Antigens

Summary Rabbits immunized with SV40 virus-transformed rabbit cells yielded antisera highly reactive in a mixed-hemadsorption assay against SV40-transformed hamster, mouse, and rabbit cells. Such antisera may prove of value in studies requiring large amounts of antibody against SV40-induced cell surface antigens.

Enhancement of Sindbis Virus Infectivity by Reduced Salt Concentration

Summary The efficiency of plaquing (EOP) on chick embryo fibroblast monolayers of three temperature-sensitive mutants of Sindbis virus defective in late functions was enhanced 10- to 11-fold when the inoculum was applied in medium containing 66% of the normal concentration of sodium chloride. Studies with one of these mutants revealed similar enhancement over a broad range of reduced salt concentrations. The EOP of wild-type virus and of a temperature-sensitive mutant defective in RNA synthesis were also enhanced, but to a lesser degree. No increase in EOP occurred if the exposure of virus to reduced salt concentration ended before the virus suspension was applied to the monolayers; thus, a virus-cell interaction appeared to be involved. The salt-sensitive step occurred within the first hr of infection, but subsequent to virus adsorption.