Mast cell sarcoma in an infant: a case report and review of the literature.

Mast cell diseases comprise a spectrum of disorders including cutaneous mastocytosis, indolent or aggressive systemic variants including leukemia, and unifocal tumor formations such as benign extracutaneous mastocytoma or aggressive mast cell sarcoma (MCS). Many mast cell diseases are associated with aberrancy of c-KIT proto-oncogene resulting in tyrosine kinase activity, typically exhibiting point mutation in codon 816. MCS is an exceedingly rare clinicopathologic entity characterized by a unifocal accumulation of neoplastic mast cells that grow in a locally destructive manner. We report a case in a 2-year-old boy who was initially diagnosed at 8 months of age with atypical cutaneous mastocytoma of the right ear with subsequent aggressive, destructive growth pattern; features that were most consistent with MCS. So far, MCS has been documented in the literature in at least 6 human cases. To the best of our knowledge, our case represents the first MCS in an infant. Thorough multimodal approach with strict follow-up is relevant in appropriately diagnosing this rare entity, particularly in differentiating this lesion from other neoplasms that are more likely to occur in infancy.

CADM1 isoforms differentially regulate human mast cell survival and homotypic adhesion.

Cell adhesion molecule 1 (CADM1), expressed by human lung mast cells (HLMCs), mediates their adhesion to airway smooth muscle (ASM), and contributes to ASM-dependent HLMC proliferation and survival. CADM1 is expressed in alternatively spliced isoforms, but those present in HLMCs and their function are not known. We cloned three functional and one cryptic non-functional isoform with alternative splicing between exons 7/11 and 1/2, respectively, from HLMCs and human MC lines (HMC-1 and LAD2). Differentiated HLMCs and LAD2 cells expressed the functional isoform SP4 containing exons 7/8/11 (~80% of clones), as well as SP1 (exons 7/8/9/11) and a novel SP6 (exons 7/8/9/10/11). In contrast, immature HMC-1 cells expressed only functional SP4. SP4 overexpression in HMC-1 cells and HLMCs augmented homotypic adhesion to a greater extent than SP1 in various conditions. In contrast, CADM1 downregulation abolished homotypic adhesion, indicating that CADM1 is the sole receptor mediating mast cell aggregation. CADM1-mediated adhesion was enhanced by the presence of cell survival factors. SP1 overexpression in HMC-1 cells compromised survival compared to SP4 overexpression or control. CADM1 downregulation resulted in reduced viability and decreased expression of the pro-survival protein Mcl-1(L), but not Blc-2 or Bcl-X(L), and increased caspase-3/7 activity in both HMC-1 cells and HLMCs. This coincided with decreased basal Kit levels in HLMCs. In summary, human MCs express multiple CADM1 isoforms which exhibit differential regulation of survival and homotypic adhesion. The most highly expressed SP4 isoform is likely to contribute to MC aggregation and longevity in mastocytosis, and augment the pathophysiology of allergic diseases.

Immunohistochemical characterization of feline mast cell tumors.

Expression of histamine, serotonin, and KIT was evaluated in 61 archived feline mast cell tumors (MCTs) from the skin (n = 29), spleen (n = 17), and gastrointestinal (GI) tract (n = 15) using immunohistochemistry. Twenty-eight percent of cutaneous MCTs, 18% of splenic MCTs, and 53% of GI MCTs displayed histamine immunoreactivity. Serotonin immunoreactivity was detected in 3 GI and 1 cutaneous MCT. Sixty-nine percent of cutaneous MCTs, 35% of splenic MCTs, and 33% of GI MCTs were positive for KIT. Expression of these biogenic amines and KIT was less common than expected. Results of this study suggest heterogeneity in feline MCTs based on anatomic location. Further studies are needed to explain the significance of these differences.

Expression of Ki67, BCL-2, and COX-2 in canine cutaneous mast cell tumors: association with grading and prognosis.

The expression of Ki67, BCL-2, and COX-2 was investigated in 53 canine cutaneous mast cell tumors (MCTs) by immunohistochemistry and quantitative real time polymerase chain reaction (qPCR) to evaluate their prognostic significance and the association with the histologic grading and the mitotic index (MI). MCTs were graded according to the Patnaik grading system and the novel 2-tier grading system proposed by Kiupel. The numbers of mitotic figures/10 high-power fields (MI) were counted. Both grading systems were significantly associated with prognosis. The Patnaik grading was of limited prognostic value for grade 2 MCTs, with 23% being associated with mortality. The concordance among pathologists was strongly improved by the application of the 2-tier grading system, and 71% of high-grade MCTs were associated with a high mortality rate. MI and Ki67 protein expression were significantly associated with grading and survival. No significant association between BCL-2 protein expression and either grading system or health status was observed. BCL-2 mRNA expression was significantly higher in grade 2 than in grade 1 MCTs, while no statistically significant differences were detected between low- and high-grade MCTs. The increased BCL-2 mRNA level was significantly associated with increased mortality rate. The COX-2 protein expression was detected in 78% of the MCTs investigated. However, neither association with the tumor grade nor with the health status was observed. COX-2 mRNA was significantly up-regulated in MCTs compared to surgical margins and control skin tissue, but it was neither associated with tumor grade nor with survival.

Secretion of pyruvate. An antioxidant defense of mammalian cells.

Cells in culture are exposed to marked oxidative stress, H2O2 being one of the predominant agents. Pyruvate and other alpha-ketoacids reacted rapidly, stoichiometrically, and nonenzymatically with H2O2, and they protected cells from its cytolytic effects. All five human and murine cell types studied, both malignant and nonmalignant, released pyruvate at an initial rate of 35-60 microM/h/2.5 X 10(6) cells when placed in 1 ml pyruvate-free medium. After 6-12 h a plateau of 60-150 microM pyruvate was attained, corresponding to concentrations reported for normal human serum and plasma. The rate of pyruvate accumulation was almost doubled in the presence of exogenous catalase, suggesting that released pyruvate functions as an antioxidant. The rate of pyruvate accumulation was dependent on cell number. Succinate, fumarate, citrate, oxaloacetate, alpha-ketoglutarate, and malate were not secreted in significant amounts from P815 cells; export was specific for pyruvate and lactate among the metabolites tested. Extracellular pyruvate was in equilibrium with intracellular stores. Thus, cells conditioned the extracellular medium with pyruvate at the expense of intracellular pyruvate, until homeostatic levels were attained in both compartments. We propose that cells plated at low density in the absence of exogenous pyruvate fail to thrive for two reasons: prolonged depletion of intracellular pyruvate and prolonged vulnerability to oxidant stress.

Multi-center, placebo-controlled, double-blind, randomized study of oral toceranib phosphate (SU11654), a receptor tyrosine kinase inhibitor, for the treatment of dogs with recurrent (either local or distant) mast cell tumor following surgical excision.

PURPOSE: The purpose of this study was to determine the objective response rate (ORR) following treatment of canine mast cell tumors (MCT) with toceranib phosphate (Palladia, SU11654), a kinase inhibitor with both antitumor and antiangiogenic activity through inhibition of KIT, vascular endothelial growth factor receptor 2, and PDGFRbeta. Secondary objectives were to determine biological response rate, time to tumor progression, duration of objective response, health-related quality of life, and safety of Palladia. EXPERIMENTAL DESIGN: Dogs were randomized to receive oral Palladia 3.25 mg/kg or placebo every other day for 6 weeks in the blinded phase. Thereafter, eligible dogs received open-label Palladia. RESULTS: The blinded phase ORR in Palladia-treated dogs (n = 86) was 37.2% (7 complete response, 25 partial response) versus 7.9% (5 partial response) in placebo-treated dogs (n = 63; P = 0.0004). Of 58 dogs that received Palladia following placebo-escape, 41.4% (8 complete response, 16 partial response) experienced objective response. The ORR for all 145 dogs receiving Palladia was 42.8% (21 complete response, 41 partial response); among the 62 responders, the median duration of objective response and time to tumor progression was 12.0 weeks and 18.1 weeks, respectively. Palladia-treated responders scored higher on health-related quality of life versus Palladia-treated nonresponders (P = 0.030). There was no significant difference in the number of dogs with grade 3/4 (of 4) adverse events; adverse events were generally manageable with dose modification and/or supportive care. CONCLUSIONS: Palladia has biological activity against canine MCTs and can be administered on a continuous schedule without need for routine planned treatment breaks. This clinical trial further shows that spontaneous tumors in dogs are good models to evaluate therapeutic index of targeted therapeutics in a clinical setting.

Determination of rates of DNA synthesis in cultured mammalian cell populations.

In cultures of a murine mastocytoma, endogenous synthesis of thymidine phosphates, as determined by the incorporation of [(3)H]deoxyuridine into DNA, was reduced within 15 min to less than 3% of control values by the addition of amethopterin (10 microM) in combination with hypoxanthine and glycine. If [(3)H]thymidine and unlabeled thymidine were added simultaneously with amethopterin, the increase with time of radioactivity in cellular DNA was linear at least between 30 and 90 min, while radioactivity in the acid-soluble nucleotide fraction remained constant during this time interval, indicating that intracellular thymidine nucleotides had the same specific activity as exogenously supplied [(3)H]thymidine. This permitted calculation of the amount of thymidine incorporated per hour into DNA of 10(6) cells. In conjunction with the base composition of mouse DNA, these results were used to calculate rates of DNA synthesis. Cell proliferation rate, cell cycle time, and the duration of the S period were not affected to any appreciable extent by the addition of amethopterin and thymidine. Rates of DNA synthesis, as derived from thymidine incorporation rates, were in good agreement with those derived from the measured mean DNA content of exponentially multiplying cells and rates of cell proliferation.

Rapid changes in nucleoside transport induced by growth inhibitors. Studies with neoplastic mast cells.

Aqueous extracts of murine embryonic or uterine tissue, or [(6)N]O(2)'-dibutyryl 3',5'-adenosine monophosphate (dbc-AMP) which were cytostatic for the murine mastocytoma P815Y in vitro also induced rapid changes in the incorporation of exogenous nucleosides into acid-insoluble material. However, these alterations were not a consequence of growth arrest. Different dose-response curves were obtained for cytostasis and inhibition of [(3)H]-nucleoside incorporation, and changes in [(3)H]thymidine uptake were detected within 15 min of treatment with the inhibitors. Also, there were differential effects of each inhibitor on the incorporation of (3)H-labeled thymidine, uridine, adenosine, or choline into acid-insoluble material.

Membrane channel formation by the lymphocyte pore-forming protein: comparison between susceptible and resistant target cells.

The assembly of pores by the pore-forming protein (perforin) of cytolytic T lymphocytes (CTLs) and natural killer cells on the membranes of different cell lines was studied. Using the patch clamp technique in the whole cell configuration, we measured the conductance increase induced by perforin in susceptible cell lines as well as in resistant CTL lines (CTLLs). The results showed that although the amplitudes of the first observed conductance steps produced in both cell types were comparable, CTLLs required at least 10-fold higher doses of perforin to form membrane pores. Outside-out patches excised from CTLL-R8, on the other hand, appeared to be more susceptible to channel formation by perforin than intact cells, as lower doses were able to induce conductance increases. Once channels were induced in CTL membranes, however, their conductances (greater than 1 nS) were indistinguishable from the ones obtained in susceptible cell lines. Fluorescence measurements with quin-2 showed that perforin induced rapid increases in the intracellular Ca2+ concentration in susceptible EL4 cells. In marked contrast, a perforin dose 60-120-fold higher than the minimal dose required to elicit Ca2+ changes in EL4 cells was not able to induce any measurable Ca2+ increase in CTLL-R8. The data suggest that the resistance of CTLs to lysis mediated by their own mediator perforin is at least in part due to their ability to avoid pore formation by this protein. The mechanism underlying this phenomenon is not yet understood, but the observation that outside-out patches excised from CTLL-R8 are more susceptible to channel formation by perforin than intact cells raises the possibility that an intracellular mechanism may be involved.

Synergistic antiproliferative effects of KIT tyrosine kinase inhibitors on neoplastic canine mast cells.

Aggressive mast cell (MC) tumors are hematopoietic neoplasms characterized by uncontrolled growth of MC and resistance to conventional drugs. In most cases, the tyrosine kinase (TK) receptor KIT is involved in malignant cell growth. Therefore, several KIT TK-targeting drugs are currently being tested for their ability to block growth of neoplastic MC. We examined the effects of four TK inhibitors (imatinib, midostaurin, nilotinib, and dasatinib) on C2 canine mastocytoma cells, as well as primary neoplastic canine MC. As assessed by (3)H-thymidine incorporation experiments, all TK inhibitors produced dose-dependent inhibition of proliferation in C2 cells with the following IC(50) values: imatinib: 269 +/- 180 nM, midostaurin: 157 +/- 35 nM, nilotinib: 55 +/- 24 nM, dasatinib: 12 +/- 3 nM. Growth-inhibitory effects of TK inhibitors were also observed in primary neoplastic mast cells, although IC(50) values for each drug varied from patient to patient, with midostaurin being the most potent agent in all samples tested. In consecutive experiments, we were able to show that TK inhibitors cooperate with each other in producing growth inhibition in C2 cells with synergistic effects observed with most drug combinations. In flow cytometry and TUNEL assay experiments, growth-inhibitory effects of TK inhibitors were found to be associated with cell-cycle arrest and apoptosis. Together, these data show that several TK-targeting drugs induce apoptosis and inhibit proliferation in canine mastocytoma cells in vitro, and that synergistic drug interactions can be obtained. Clinical trials are now warranted to explore whether these TK inhibitors also counteract growth of neoplastic cells in vivo in patients with aggressive MC tumors.

Dog mastocytoma cells produce transforming growth factor beta 1.

Transforming growth factor-beta (TGF beta) promotes deposition of extracellular matrix and is associated with fibrotic conditions both in experimental animals and in humans. Although a role for mast cells has been suspected in the pathogenesis of fibrosis, no potent mediator capable of stimulating fibroblast growth or extracellular matrix deposition has been identified in mast cell supernatants. We report here the constitutive production of TGF beta 1 by four dog mastocytoma cell lines. TGF beta 1 was identified by characteristic biologic activity, blockade of biologic effect by specific neutralizing antibody, and by recognition of a band with the appropriate migration by western blot. TGF beta 1 mRNA, but not TGF beta 2 or TGF beta 3 mRNA, was also produced constitutively by all four cell lines. Quantitation by bioassay revealed baseline TGF beta secretion of approximately 1 ng/10(6) cells over 48 h. Stimulation of mastocytoma cells with phorbol ester increased the rate of release of TGF beta 1, most markedly in the first 30 min after stimulation, without increasing TGF beta 1 mRNA. Dog mastocytoma cells produced TGF beta 1 primarily in a latent form, inactive until treated with acid. Both pure TGF beta 1 and TGF beta-containing mastocytoma cell-conditioned media inhibited mitogenesis and proliferation in dog mastocytoma cell lines, suggesting that mast cell tumor lines would not grow preferentially based on their ability to produce TGF beta. These studies may make possible further investigation of the mechanism by which mast cells contribute to the induction of fibrosis.

Hydrogen peroxide from cellular metabolism of cystine. A requirement for lysis of murine tumor cells by vernolepin, a glutathione-depleting antineoplastic.

The sesquiterpene lactone antineoplastic vernolepin acutely depletes murine tumor cell glutathione (GSH), and lyses the cells by an unknown mechanism that is enhanced synergistically by inhibition of GSH synthesis with buthionine sulfoximine (BSO) (Arrick et al. 1983. J. Clin. Invest. 71:258). We found here that lysis of P815 mastocytoma cells by vernolepin, with or without BSO, required cystine in the culture medium. Addition of catalase markedly suppressed vernolepin-mediated cytolysis in cystine-containing media, suggesting the involvement of hydrogen peroxide in the cytolytic action of vernolepin. Consistent with this, inhibition of tumor cell glutathione disulfide reductase with 1,3-bis(2-chloroethyl)-1-nitrosourea or inhibition of endogenous catalase with aminotriazole synergistically augmented cytolysis by vernolepin. Moreover, H2O2 was released by suspensions of P815 cells in cystine-containing buffer (63 pmol/10(6) cells X h). Omission of cystine reduced the rate of H2O2 accumulation 10-fold. No H2O2 was detected without cells. Cytolysis by vernolepin could be restored in cystine-deficient medium by several other disulfides, themselves noncytolytic, such as disulfiram and oxidized Captopril, as well as by cysteine. In contrast, withholding two other essential amino acids (leucine or tryptophan) or adding cycloheximide did not interfere with cytolysis by vernolepin. These results suggest that cellular uptake of disulfides of physiologic and pharmacologic interest may be followed by their intracellular reduction and autooxidation with generation of H2O2. This previously unrecognized source of intracellular oxidant stress may be an important component of injury to GSH-depleted cells.

Isotope-release cytotoxicity assay with the use of indium-111: advantage over chromium-51 in long-term assays.

The adaptation of indium-111-oxine (also known as 8-hydroxyquinoline) (111In Ox) chelate for long-term (18-48 hr) isotope-release assays of cell-mediated cytotoxicity (CMC) and its advantages over the use of 51 Cr are described. Labeling of DBA/2 P815 mastocytoma cells with 111InOx resulted in the incorporation of as many as a million counts per minute in 10(5) cells with no reduction in cell viability. 111InOx labeled both mouse and human tumor cells. 111InOx, like 51Cr, primarily labeled cytoplasmic constituents; up to 80% of the label existed in a releasable form. 111InOx was quantitatively released from labeled P815 in response to specifically sensitized C57BL/6 lymphocytes. The high labelling efficiency of 111InOx offered a significant advantage over 51Cr in 18- to 48-hour assays for CMC by reducing the counting error and thus making the assay more precise. Because of its higher labeling efficiency, 111InOx can be used in microcytotoxicity assays. 111InOx has the added advantage of a lower spontaneous release in culture than 51Cr. This feature of 111InOx also makes the calculation of specific isotope release more accurate than that achieved with 51Cr in long-term cytotoxic assays.

Antigenic changes of DBA/2J mastocytoma cells when grown in the BALB/c mouse.

A 10-day growth period of the DBA/2J strain-specific P815-X2 mastocytoma in the BALB/c mouse altered the antigenicity of the tumor cell surface. The in vivo-modified mastocytoma cells differed from mastocytoma cells grown in the original DBA/2J mice in suspectibility to lysis by immune peritoneal exudate cells, in vitro antigenic recognition by cytotoxic T-cells, and immunizing capacity in allogeneic C57BL/6 mice. Propagation of the altered tumor cells in the original host or maintenance in tissue culture for 40 hours restored complete susceptibility to lymphocyte-mediated cytotoxicity.

Canine mast cell tumors: correlation of apoptosis and proliferation markers with prognosis.

The Patnaik histologic grading system is commonly used to predict the behavior of cutaneous mast cell tumors (MCTs) in dogs, but it is less useful for grade 2 MCTs because they exhibit considerable variation in biological behavior. In this retrospective study, immunohistochemical staining for Ki-67, proliferating cell nuclear antigen (PCNA), and survivin and a standardized argyrophilic staining of nucleolar organizer regions (AgNOR) protocol were performed on 121 archived paraffin-embedded specimens of canine cutaneous MCTs, for which clinical follow-up data were available. Cox regression models indicated that the Ki-67 score (hazard ratio, 1.92; P < .001) and mean AgNOR score (hazard ratio, 2.57; P < .001) were significantly associated with Patnaik grade and survival time. A binary Ki-67 variable (cutoff point Ki-67 score = 1.8) was a significant predictor of survival for dogs with grade 2 MCTs. The estimated 1-, 2-, and 3-year survival probabilities for dogs with grade 2 MCTs and Ki-67 scores less than 1.8 were 0.92, 0.86, and 0.77, respectively (SEs, 0.08, 0.14, and 0.23, respectively; median not estimable). The corresponding survival probabilities for dogs with grade 2 MCTs and Ki-67 scores higher than 1.8 were 0.43, 0.21, and 0.21, respectively (SEs, 0.19, 0.18, and 0.18, respectively; median survival time, 395 days). No significant association was identified between survival and survivin score or PCNA score. This study shows that both mean AgNOR score and Ki-67 score are prognostic markers for canine MCTs. The Ki-67 score can be used to divide Patnaik grade 2 MCTs into 2 groups with markedly different expected survival times.

Elevated transcriptional complexity and decrease in enzymatic DNA methylation in cells treated with L-ethionine.

This paper analyzes the extent of enzymatic methylation of DNA in P815 cells cultured for several cell cycles in the presence of 1 mM L-ethionine by use of the bacterial restriction enzymes HpaII, MspI, HhaI, HaeII, and AvaI. The results obtained suggest that the extent of methylation of DNA is decreased during L-ethionine treatment and that the degree of this inhibition varies among different methylation sites. The nucleotide sequence complexity of nuclear RNA in P815 cells was analyzed by excess hybridization with tracer amounts of nick-translated nonrepetitive P815 [3H]DNA sequences. About 6.2% of the nonrepetitive sequences form hybrids with nuclear RNA of controls cells, whereas 8.8% are complementary to nuclear RNA from L-ethionine-treated cells. Thus, the decrease in enzymatic DNA methylation correlates with the presence of new transcriptional products suggesting that this modification process inversely correlates with the initiation of transcription.

Arachidonic acid, a growth signal in murine P815 mastocytoma cells.

Evidence is presented that inducing P815 murine mastocytoma cells to grow with serum activates a Ca(2+)-stimulated phospholipase A2 and the rapid release of arachidonic acid by the cells. Slower growth was also maintained by arachidonic acid or its immediate precursors or by diacylglycerols when bovine serum albumin replaced the serum. Together, arachidonic acid and 1-oleoyl-2-acetylglycerol stimulated growth at the same rate as 10% serum consistent with a role for both arachidonic acid and protein kinase C in the response to serum. Arresting cell growth with N6,O2'-dibutyryladenosine 3',5'-cyclic phosphate and theophylline inhibited the release of arachidonic acid in response to serum, suggesting that cyclic AMP prevents phospholipase activation as one of its pleiotypic effects on growth. Attempts to demonstrate metabolism of [3H]arachidonic acid to eicosanoids in serum-treated P815 cells by high-performance liquid chromatography or thin layer chromatography were unsuccessful, with the major products being phospholipids and triacylglycerol. Incubating digitonin-permeabilized P815 cells with [gamma-32P]ATP and arachidonic acid rapidly increased the phosphorylation of some proteins in the cells, especially the M(r) 135,000 and M(r) 44,000 proteins which were considerably more phosphorylated than the rest. Phosphorylation of these proteins was not prevented by several inhibitors of protein kinase C, nor was it increased by diacylglycerols or phorbol ester, suggesting that arachidonic acid activates a growth-related protein kinase other than protein kinase C in P815 cells. The possibility that some polyunsaturated fatty acids may promote tumor cell growth by stimulating protein phosphorylation is considered.

Effects of Tumor-like assay conditions, lonizing radiation, and hyperthermia on immune lysis of tumor cells by cytotoxic T-lymphocytes.

Cytotoxic T-lymphocytes (CTL's) harvested from mixed splenic lymphocyte cultures (DBA/2 + C57BL) were tested for their ability to lyse allogeneic P815 mastocytoma cells under various tumor-like assay conditions, with or without previous exposure to ionizing radiation or hyperthermia (43 degrees). There was little or no decrease of immune cytolysis when CTL's were assayed by 51Cr release under tumor-like conditions (plateau-phase target cells, low pH, or anoxia) or after irradiation, but cytolytic activity was greatly reduced when CTL's were exposed to heat; 45 min of hyperthermic treatment decreased activity by greater than or equal to 99% while reducing the apparent cell viability (as indicated by trypan blue exclusion) by only 30%. When the P815 target cells rather than the CTL's were exposed to heat their susceptibility to immune lysis was not affected even after treatment times that were lethal to the tumor cells. Despite the dissimilar heat sensitivities of CTL and P815 cells, the dose-response curves for inhibition of protein synthesis by heat, as indicated by [3H]leucine incorporation, were similar for both cell types: neither the depression of protein synthesis in heated CTL's nor the decreased cytolytic ability of these cells was reversed within 3 hr. When irradiated or heated P815 cells were incubated with CTL's, the resulting survival curves were always additive, indicating that neither irradiation nor heat treatment affected the susceptibility of the tumor cells to immune attack. The extreme heat sensitivity of cytotoxic T-lymphocytes raises important questions about the possible effects of hyperthermic treatment on the immune competence of cancer patients.

Glycolipid-anchored IL-12 expressed on tumor cell surface induces antitumor immune response.

Systemic or local administration of cytokine has been used as a mode to enhance the antitumor immune response induced by many cancer vaccines. We have investigated whether the expression of cytokines on the tumor cell surface as a glycolipid (GPI)-anchored form will be effective in inducing antitumor immune response using a GPI-anchored interleukin (IL)-12 (GPI-IL-12) as a model. GPI-IL-12-induced the proliferation of concanavalin A-activated T cells and induced IFN-gamma secretion by activated and allogeneic T cells, indicating that the membrane-expressed IL-12 can stimulate T cells. GPI-IL-12 expressed on the tumor cell surface prevented tumor growth in mice in a highly tumorigenic murine mastocytoma model. These results suggest that the cell surface-expressed GPI-IL-12 can be effective in inducing antitumor immune response, and GPI-anchored cytokines expressed on the tumor cell surface may be a novel approach to deliver cytokines at the immunization site during vaccination against cancer. Furthermore, purified GPI-anchored cytokines can be used to quickly modify tumor membranes by the protein transfer method to express the desired cytokines for vaccine development.