Studies on the histochemical “leucine aminopeptidase” reaction

Summary Cathepsin B has been purified by gel filtration. A complete separation from cathepsin C and D was achieved. This particular proteinase hydrolysed the chromogenic substrates BANA and LNA. Cathepsin B must thus be included among the potential initiators of a positive histochemical LNase reaction.Supported by grants from the Jubilee Fund, Cancer Society of Stockholm and the Swedish Natural Research Council.     

Fatty acid synthesis inTrichophyton rubrum

Analysis of the fatty acid content ofT. rubrum showed that the organism is capable of synthesizing a variety of saturated and unsaturated long-chain fatty acids (Kostiw, Vicher &Lyon, 1966). The present study was undertaken to determine the mechanism of synthesis of these fatty acids. Experimental data point to the presence of two mechanisms of fatty acid synthesis inT. rubrum:de novo synthesis and chain elongation. The presence of both mechanisms is suggested by the nature of the enzyme preparation, by the cofactor requirements for either pathway, and by the reaction products.University of Illinois at the Medical Center, and Chicago Medical School, Chicago, Illinois. Presented in part at the International Society of Mycology Meeting, New Orleans, Louisiana, August 1967.     

A comparative study of cytoplasmic basophilia and the population density of ribosomes in the secretory cells of mouse seminal vesicle

Summary A comparative cytochemical and electron microscopic study on the ergastoplasm in the secretory cells of the seminal vesicles of castrated, normal, and testosterone-treated mice is reported. Castration induced a progressive decline in cytoplasmic basophilia (identified with ribonucleic acid) and testosterone treatment caused an enhancement over the normal level. There were corresponding changes in total area of ergastoplasmic membranes, but the expected changes in population density of ribosomes (ribonucleoprotein particles) in the intercisternal cytoplasm did not occur. These observations conflict with the currently-accepted view that almost all of the ribonucleic acid responsible for cytoplasmic basophilia in adult mammalian cells is contained in the ribosomes.Other changes in the fine structure of these cells in the experimental animals are briefly described.This research was aided by grants from the American Cancer Society and the United States Public Health Service (B-2145). Preliminary reports were made at the Tenth Annual Meeting of the Histochemical Society (Deane and Porter 1959) and the Tenth International Congress for Cell Biology (Deane and Porter 1960).     

Cylindrical structures in the chloroplasts of Sirogonium melanosporum

Summary Cylindrical structures with outside diameters of 390 to 410 Å have been observed in the chloroplasts of mature vegetative cells of the filamentous, green alga Sirogonium melanosporum. These cylindrical structures are either parallel to one another or randomly oriented in the stroma matrix of the chloroplast. Some of the outer cylindrical structures of the complex appear to be continuous with thylakoid membranes, suggesting a relationship between these two structures.This work was supported by an Institutional Grant from the American Cancer Society to the University of Arizona and by grant GB2440 from the National Science Foundation to R. W. Hoshaw. The authors thank Dr. Wayneferris for the use of the electron microscope supported by NSF grant GB3330.     

Altered growth kinetics precede calcium-induced differentiation in mouse epidermal cells

Summary Primary cultures of newborn mouse epidermal cells proliferate rapidly and with a high growth fraction for several months when grown in medium with low calcium (0.02 to 0.1 mM). Addition of calcium to levels generally used in culture medium (1.2 mM) was followed by rapid changes in the pattern of proliferation. By using a combination of technics (a stathmokinetic method, autoradiography, [³H]thymidine incorporation into DNA, DNA flow cytometry) it was found that cell flux was blocked for 5 to 6 h, followed by a short rise in the mitotic rate at 10 h, and a gradual fall in all growth parameters until about 32 h after the calcium switch. There was no accumulation of cells in any particular cell cycle phase. The results indicate that the calcium switch is followed by a strong reduction in cell flux from G₁ whereas the majority of the cells that had left G₁ at the time of the switch completed one cell division before cessation of all proliferative activity. Both before and after the switch the primary epidermal cultures consisted of one diploid and one tetraploid G₁ DNA stemline that seemed to react in the same way to calcium. This work reported in this paper was undertaken during the tenure of an American Cancer Society-Eleanor Roosevelt-International Cancer Fellowship awarded by the International Union Against Cancer (K. E.). The project was supported by funds partly provided by the International Cancer Research Data Bank Program of the National Cancer Institute, National Institutes of Health, Bethesda, MD, under contract N01-C0-65341 (International Cancer Research Technology Transfer) and partly by the International Union Against Cancer (O.P.F.C.).     

Organ culture of adult rat colonic mucosa on fibrin foam

Summary A system for maintaining adult rat colonic mucosa in organ culture for up to 28 days is described. Distal colonic mucosa physically separated from the muscle layers was cultured at 37°C on a substrate of human fibrin foam in HEPES- and bicarbonate-buffered Waymouth's MB 752/1 medium supplemented with 10% fetal bovine serum,l-glutamine, bovine albumin, ascorbic acid, hydrocortisone, insulin, and ferrous sulfate; the optimal atmosphere for culture was 95% O₂ and 5% CO₂. Viability of explants was demonstrated by tissue morphology with light microscopy, incorporation of [³H]thymidine and [³H]leucine into DNA and protein, [¹⁴C]glucosamine and [³H]fucose incorporation, and glycoprotein synthesis. Two days after initiation of culture, degeneration of surface and crypt cells was observed. Secreted mucosubstances covered the explants. Explants maintained in 95% O₂ retained a variable number of glandular crypts with normal columnar epithelium for 14 to 21 days in culture. At 28 days, explants contained a single layer of cuboidal surface epithelium and a rare cryptlike gland. This work was supported by the National Cancer Institute Contract N01-CP-75953 and in part by the International Cancer Research Data Bank Program of the National Cancer Institute, National Institutes of Health, under Contract N01-CO-65341 with the International Union Against Cancer.     

Autoradiographic and microspectrophotometric studies of DNA synthesis in excised tobacco pith tissue

Summary Pith tissue was cultured on modified White’s nutrient medium supplemented, except for controls, with 2 mg/l of IAA and/or 0,5 mg/l of kinetin. For autoradiographs sections were used from tissue grown on medium containing tritiated thymidine. Nuclear DNA contents (Feulgen) were measured by the microspectrophotometric two-wavelengths method. No fading of Feulgen dye in nuclei was found in 11 weeks, in contrast to considerable fading observed in earlier work when a different batch of basic fuchsin had been employed. Counts of radioactive nuclei in autoradiographs agreed well with microspectrophotometric results on the occurrance of DNA synthesis. In control cultures, with or without tritiated thymidine, DNA doubling took place in about 20% of the nuclei during the first two days but in few, if any, thereafter. It was confirmed that kinetin, as well as IAA, increases the frequency of nuclei undergoing DNA synthesis. However, IAA, in contrast with kinetin, still induced considerable DNA doubling after two days. Continued cell reproduction was maintained only in the presence of both substances. This work has been supported in part by research grants toK. Patau from the US Public Health Service (grant No. C-3313) and the American Cancer Society; and by grants toF. Skoog from the American Cancer Society and the Research Committee of the University of Wisconsin Graduate School with funds from the Wisconsin Alumni Research Foundation.     

Learning how to learn: The significance and current status of learning set formation

In honor of the memory ofHarry F. Harlow, this paper reviews the current status of learning set formation, the discovery of which represents one ofHarlow's major contributions to behavioral science. Learning set formation or “learning how to learn” refers to the learning of visual and other types of discrimination problems progressively more quickly as a function of training on a series of such problems. The general procedure thatHarlow used, his original learning set finding, and its significance are described first. A brief review of theories of learning set formation follows. Lastly, the attempt to use learning set formation as a tool for studying comparative behavior is discussed. This article is based on a paper by the author delivered at:A. M. Schrier andS. J. Suomi (cochairs),Primate Behavior: A Symposium in Memory of Harry F. Harlow. Symposium presented at the IXth Congress of the International Primatological Society, Atlanta, Georgia, August 1982.     

Crucial demonstration of the proliferative growth regulating property of the naturally occurring chemical equilibrium composed of sulfhydryl and its partially oxidized derivatives

Summary and conclusion Four experimental criteria have been set up which are essential for the postulate that growth by increase in cell number is regulated by the naturally occurring chemical equilibrium composed of the sulfhydryl group and its partially oxidized derivatives.It has been shown that two of these have already been satisfied, and that a third can be considered as indirectly established. Report is made of an experiment which discharges the fourth.The cumulative data thus lead to the conclusion that the postulate is a true expression of a basic biological principle.Grateful acknowledgement should be given to the International Cancer Foundation established by Mr. Wm. H.Donner of Philadelphia for support in this work.These experiments were done at The Marine Experiment Station of The Research Institute of The Lankenau Hospital, North Truro, Massachusetts, under grants from Mr.August Bein of Philadelphia, and the Capt. L. D.Baker Estate of Boston and Wellfleet.     

Localization of melanin synthesis within the pigment cell: Determination by a combination of electron microscopic autoradiography and topographic planimetry

Summary Localization of melanin synthesis within the pigment cells of the Cloudman S-91 mouse melanoma was determined by means of a combination of high resolution autoradiography and topographic planimetry. Initial melanin biosynthesis occurred predominantly in the endoplasmic reticulum and associated ribonucleoprotein particles of the melanocytes. By measuring a number of cell organelles and employing the index of relative specific localization it could be shown that the nucleus and mitochondria are of little or no importance in the process of melanogenesis.This investigation has been supported by the following research grants: CA 06548 CB, NIH, PHS and an Institutional Grant from the American Cancer Society (to H. M. H.); CA-05887, NIH, PHS (to A. S. Z.); M-00388 and NB-00782, NIH, PHS (to J. F. H.). One of us (H. M. H.) holds a Research Cancer Development Award (5-K 3-GM-2634) of the National Institute of General Medical Sciences, Public Health Service.We are grateful to Mr. Ronald Abler for his help with the topographic measurements; to Dr. Erhard Haus for help and advice; to Mr. J. Thornby and Mr. A. P. Basu for assistance with the statistical aspects of this study; and to Mrs. Lenore Mottaz, Miss Bernice Uittenbogaard, and Mrs. Judith Strong for careful technical assistance.     

The antigenicity of regenerating tail tissue in the newt Diemictylus viridescens

Young adult male rabbits were inoculated with antigens prepared from regenerating (blastema stage) and nonregenerating tail tissues of the newtDiemictylus viridescens. Blood was collected from these rabbits after six weeks of semiweekly injection, two weeks of respite, and two more weeks of injections. A Freund adjuvant was added to the antigen preparations at the time of injection in order to elicit the anamnestic effect.Ouchterlony agar diffusions of the newt antigen preparations vs. the rabbit antisera were carried out. The resulting patterns of precipitation bands were compared and photographed.The strongest precipitation reactions of a given series were those between the antigen preparations made from nonregenerating tissue and their homologous antisera. The weakest reactions occurred between regenerating tissue antigens and regenerating tissue antisera. The strength of the antigen-antibody reactions was judged by the number of bands appearing in the diffusion plate and by the distinctness of these bands. Reactions of intermediate strength occurred between regenerating antigens and nonregenerating antisera, between nonregenerating antigens and regenerating antisera, and between antigens and antisera of different series.The loss of antigenicity during the blastemal period was considered to be related to the destruction of tissue in the wound areas at this time, and to indicate a quantitative rather than a qualitative loss of protein in regenerating tissue.This work is taken from data submitted to the Department of Biology of Fordham University in partial fulfillment of the requirements for the degree of Doctor of Philosophy, and was supported in part by a grant from the New York City Cancer Committee of the American Cancer Society.The author acknowledges his indebtedness to Dr.Alexander Wolsky of Fordham University, under whose direction this investigation was carried out, and Dr.John J. Corbett of Manhattan College and Lederle Laboratories.     

An aryl β-d-glucosidase of the aquatic fungus Lagenidium giganteum,a parasite of mosquito larvae

Lagenidium giganteum Couch, a watermold parasitic on mosquito larvae possesses an intracellular -d-glucosidase (-d-glucoside glucohydrolase, E. C. 3.2.1.21). The enzyme was purified 132 fold and, with the substrate p-nitrophenyl -d-glucoside, was shown to have the following properties: The pH of optimum enzyme stability and activity lay between 5.5 and 6.0, and the enzyme was inactivated at temperatures above 50°C. The K _m was 4.6×10^-5 M and the Arrhenius activation energy was 8.35 Kcal·mole^-1. Elution from Sephadex G-200 gave an approximate molecular weight of 120000. The enzyme was inhibited by Pb²⁺, Ag²⁺ and Hg²⁺, by glucose and by p-chloromercuribenzoate. The latter inhibition was overcome cy cysteine. Chromatographic studies demonstrated transferase as well as hydrolase properties.This paper represents a portion of a Ph.D. dissertation presented by T. M. McInnis, Jr., to the University of North Carolina at Chapel Hill. The work was supported in part by grants from the American Cancer Society, the University of North Carolina Research Council, the Society of Sigma Xi, and a United States Army Medical Research DevelopmentGrant DADA 17-72-C-2168.     

Activity manifestations of Hassall's corpuscles in vitro as revealed by cinematography

Summary Thymic explants from newborn rats were cultivated in Rose chambers under dialysis membranes. With the use of phase contrast, time-lapse cinematography, the following activity manifestations were observed: 1. Several corpuscles showed rotatory movements; 2. nuclear rotation was observed in some cells of the corpuscles; 3. some individual cells in the 15-day culture showed pulsatile activity which might be involved in the mechanism of the rotatory movements of the cellular aggregates; 4. the corpuscles increased in size by the addition of cells and/or by mitosis; 5. the elements at the periphery of the more mature corpuscles (7- and 9-day cultures) were viable, while the central area appeared to be composed of necrotic tissue or hyalinized material.Grateful acknowledgement is made to Dr. C. M. Pomerat for encouragement in the course of this study. Mr. Charles Raiborn aided in the preparation of cultures and Messrs. C. G. Lefeber and Robert Olson rendered indispensable assistance with the photographic work.Aided by an American Cancer Society Student Fellowship (USC-IDC) and in part by Grant No. G-14091 from the National Science Foundation administered by C. M. Pomerat.     

Preparation of tissues for localization of sex hormones by autoradiography

Summary The intracellular localization of ³H-oestradiol in various tissues was examined. For this purpose standard autoradiograms were prepared after freeze drying, osmium vapour fixation and Epon embedding. The radioactive material showed a preferential localization in all the tissues studied, viz. uterus, vagina and anterior pituitary gland. In all tissues a major proportion of the radioactivity was associated with the cell nuclei. Radioactive labelling outside the cell boundaries and in the surrounding connective tissue was almost lacking. Likewise, a very low number of silver grains were found over the Epon in the clefts and at the margin of the tissue sections. The observations appear to indicate that the diffusion and probably also the intracellular dislocation of the radioactive material are very limited.The validity of the results was examined. Pre- and postmortem changes, rapid freezing and osmium vapour fixation were not observed to influence the localization of the radioactivity. Furthermore, the localization was the same whether embedding was carried out at –10°C or at 50°C.It is concluded that freeze drying, osmium vapour fixation and Epon embedding provide a valid method for accurate intracellular localization of steroid sex hormones.This work was supported by grants from The Norwegian Cancer Society and by Nordisk Insulinfond. The skilful assistance of Miss Helga Friedl and Mrs. Jane Larsen is gratefully acknowledged.     

Observations on the application to electron microscopy of the lead phosphate technique for the demonstration of acid phosphatase

Summary The effects of formaldehyde and glutaraldehyde fixation, preparation of frozen sections 50 thick, and incubation in Gomori medium for acid phosphatase on the appearance of parenchymal cells of mouse liver and of the cells of the proximal convoluted tubules of the rat kidney were studied by electron microscopy. Following these procedures very slight changes occurred in glutaraldehyde-fixed tissues, whereas the preservation of the tissue after formaldehyde fixation in general was inferior. A number of factors influencing the results of the Gomori lead phosphate method as applied to electron microscopy were studied and discussed, and a technique was described permitting precise localization and reproducible results on the ultrastructural level. The significance of the results was discussed in relation to presumed artifactual localizations and to the limitations on the significance of the findings caused by the effects of the preparatory procedures, with special reference to the fixation in aldehyde.This investigation was supported in part by a research contract, Project Number DA 49-193-MD-2379 (MG 30.2084), from the Medical Research and Development Command, U. S. Army, Washington, D. C. 20315; by American Cancer Society Grant E-201; by the Swedish Cancer Society; and by the Board of Swedish Life Insurance Companies.Dr. Ericsson was a fellow of the Dillon Fund in 1962, on temporary leave from the Karolinska Institute, when part of this study was performed.     

Preparation and structure-activity relationship of reagents for cytochrome oxidase activity: potential for light and electron microscopy

Summary The syntheses of a series of p-substituted aromatic diamines and some representative thioureido- and mercapto-naphthols are described. Their cytochemical behavior in the Nadi reaction using fresh frozen sections of rat heart was studied in an attempt to learn more about the structural requirements of the Nadi reaction for cytochrome oxidase.The lipid solubility of the dyes formed from either N,N-dimethyl-p-phenylenediamine or ADN (4-amino-1-N,N-dimethylnaphthylamine) with 1-naphthol can be decreased by substituting hydrophilic hydroxyethyl or dihydroxypropyl side chains for one or more of the methyl groups in these reagents. However, these dyes diffuse readily, fade rapidly and are too soluble in water as well as lipid, which renders them unsuitable for light and electron microscopy.Burstone's reagent PPD (N-phenyl-p-phenylenediamine) and ADN (4-amino-1-N,N-dimethylnaphthylamine) are capable of undergoing self condensation either alone or in the presence of an unreactive naphthol to give colored indamines which osmicate readily. Blocking either the 4-position of N-phenyl-p-phenylenediamine, the secondary amino group, or both of these positions, with a methyl group did not prevent indamine formation.N-Benzyl-, N-4-methylbenzyl- and N-4-methoxybenzyl-p-phenylenediamine are good reagents for the demonstration of cytochrome oxidase activity in the Nadi reaction with light microscopy. They produce blue indoaniline dyes with 1-naphthols and do not self condense to form highly colored pigments. These indoanilines are osmiophilic eliminating the necessity for introducing osmiophilic groups for electron microscopic studies. Their drawback in electron microscopy is in the droplet nature of the deposit.Incorporating a carbonyl or carboxyl function into the 2-position or a bulky substituent into the 5-position of 1-naphthol prevented indoaniline formation.A new method for the cytochemical demonstration of cytochrome oxidase is presented utilizing a new reagent N,N-bis(p-aminophenyl)-1,3 xylylenediamine (XIII) (BAXD). This reagent is polymerized to an insoluble osmiophilic polymer distributed in non-droplet form, thus providing a useful method for demonstrating cytochrome oxidase activity in light and electron microscopy.This investigation was supported by a research grant (CA-02478) from the National Cancer Institute, U.S. Public Health Service, Bethesda, Maryland. Presented (in part) as a Presidential Address (AMS) at the Third International Congress of Histo- and Cytochemistry on August 19, 1968 in New York, N.Y. Acknowledgement is due Lionel, Katzoff for preparation of the thiolnaphthols XXXV and XXXVI, and to Norberto I. Schinitman for the osmium analysis.     

d-ephedrinephosphate,DEP: A new substrate with specificity for prostatic acid phosphatase (PAP)

Summary This report describes the synthesis and physical (including spectral) properties of a new substrate, d-ephedrinephosphate, DEP¹, which is histochemically highly specific for a secreted non-lysosomal prostatic acid phosphatase, PAP. This specificity is in contrast to other substrates which are nonspecific, i.e., which demonstrate acid phosphatases that originate from various cell types and are mainly lysosomal. When this substrate is used for light and electron microscopic histochemistry in a modified Gomori medium, PAP is demonstrated mainly in secretory granules and in the Golgi apparatus (and its related vacuoles) of prostatic epithelial cells of several species of mammals including man. This corroborates our previous suggestion that PAP is not a lysosomal enzyme as are many of the other acid phosphatases. This high degree of specificity of DEP for PAP supports the usefulness of this compound in the histochemical and biochemical characterization of PAP, and in the diagnosis of localized or disseminated prostatic disease.This investigation was supported by research grants CA-02478 from the National Cancer Institute, NIH, U.S. Public Health Service, Bethesda, MD and CA-16077 the National Prostatic Cancer Project, NCI, Buffalo, NYDedicated to the memory of the late Arnold M. Seligman, M.D., American Cancer Society Professor of Research Oncology and Cell Biology, who pioneered the development of modern enzyme cytochemistry and under whose direction part of this work was initiated     

Distribution of mitochondria in pyramidal cells and boutons in hippocampal cortex

Summary The amount of mitochondria has been recorded in various parts of neurons. This was done in electron micrographs of cerebral cortex from the hippocampal region. The outlines of boutons, somata and dendrites of varying diameters were transferred to tracing paper together with the outlines of the contained mitochondria. The same was done for whole tissue for comparison. After cutting out and weighing the outlined areas, the fraction of the various tissue constituents, or of whole tissue, occupied by mitochondria was determined. The absolute values are shown in the illustrations (Figs. 4–9). The dendritic shafts of pyramidal cells, coursing through stratum radiatum of regio superior (CA 1), are particularly poor in mitochondria (about 2%). In the branches, the amount as a rule increases with decreasing diameter (to nearly 13% in stratum moleculare).Boutons were the structures richest in mitochondria, but the amount varied with location.This study was supported in part by Grant NB 02215 from the National Institute of Neurological Diseases and Blindness, U.S. Public Health Service. The authors are indebted to Mrs. J. L. Vaaland, Miss M. Johansen and Mr. B. V. Johansen for valuable technical assistance.Fellow of The Norwegian Cancer Society during part of this study.     

Mouse mammary cells ind-valine medium

Summary Cells of a mouse mammary epithelial cell line as well as fibroblasts from a mouse mammary explant were severely inhibited from proliferating in a medium in whichd-valine was substituted forl-valine. After the first few days ind-valine medium, the number of epithelial cells did not increase despite the fact that a few percent continued to synthesize DNA. The cells did recognize the presence of thed-valine in the medium because cells ind-valine increased in volume and their numbers remained stationary, whereas cells without valine shrank and the cell numbers decreased with time. The NMuMG cells were obtained from Mr. Robert Owens and were produced with support from the National Cancer Institute, Biological Carcinogenesis Branch, Division of Cancer Cause and Prevention under the auspices of the Office of Naval Research and the Regents of the University of California. This project was funded by the National Cancer Institute, Bethesda, MD, Contract N01-CB-74094.     

Phorbol ester-induced enhancement in lytic activity of CD8+ splenic T cells from low-dose melphalan-treated MOPC-315-tumor bearers

Summary We have previously shown that while spleen cells from untreated mice bearing a large MOPC-315 tumor are not cytotoxic in vitro for MOPC-315 tumor cells, spleen cells obtained from such mice on day 7 after low-dose melphalan (l-phenylalanine mustard);l-PAM therapy exert a substantial anti-MOPC-315 cytotoxicity [Mokyr et al. (1989) Cancer Res 49: 4597]. Here we show that this anti-MOPC-315 lytic activity is evident by day 5, and peaks on day 7 after the low-dose chemotherapy, at a time when the mice are actively engaged in tumor eradication. Short-term exposure of spleen cells from mice bearing a MOPC-315 tumor and treated with low-dosel-PAM (l-PAM TuB mice) to phorbol 12-myristate 13-acetate (PMA) was found to enhance greatly the ability of these spleen cells to lyse MOPC-315 tumor cells. The highest level of anti-MOPC-315 cytotoxicity was obtained when spleen cells from tumor-bearing mice that had received chemotherapy 7 days earlier were exposed to PMA at a concentration of 1–10 ng/ml. The exertion of the enhanced anti-MOPC-315 lytic activity byl-PAM TuB spleen cells exposed to PMA was found to require CD8⁺, but not CD4⁺, T cells. The apparent specificity of the lytic activity exerted by the PMA-stimulatedl-PAM TuB spleen cells was illustrated not only by the inability of the spleen cells to lyse an allogeneic, antigenically unrelated thymoma (EL4), but also by their relatively weak lytic activity for two antigenically related syngeneic plasmacytomas. In addition, when EL4 target cells were admixed with MOPC-315 tumor cells, the lytic activity triggered in thel-PAM TuB spleen cells by the MOPC-315 tumor cells plus PMA was not effective in lysing the antigenically unrelated target cells. Moreover, even in the presence of the calcium-specific ionophore, ionomycin,l-PAM TuB spleen cells exposed to PMA were unable to lyse the EL4 target cells. Thus, fresh CD8⁺ splenic T cells froml-PAM TuB mice that are in the process of eradicating a large MOPC-315 tumor as a consequence of low-dosel-PAM therapy can be triggered with PMA to exert enhanced lytic activity against MOPC-315 tumor cells. Since the curative effectiveness of low-dose chemotherapy for MOPC-315 tumor-bearing mice requires the participation of CD8⁺ T cells that exploit a cytotoxic T lymphocyte type lytic activity for tumor eradication, it is feasible that in some situations PMA-like stimulants could be used to augment the antitumor cytotoxic activity of the CD8⁺ T cells, which in turn could improve the therapeutic outcome of low-dose chemotherapy.Supported by research grant IM-435A from the American Cancer Society and research grant B-8806 from the Bane EstateIn partial fulfillment of the requirements for the Doctor of Philosophy DegreeRecipient of Career Development Award CA-01 350 from the National Cancer Institute