Evidence of mTOR Activation by an AKT-Independent Mechanism Provides Support for the Combined Treatment of PTEN-Deficient Prostate Tumors with mTOR and AKT Inhibitors.

Activation of the phosphoinositide 3-kinase pathway is commonly observed in human prostate cancer. Loss of function of phosphatase and tensin homolog (PTEN) is associated with the activation of AKT and mammalian target of rapamycin (mTOR) in many cancer cell lines as well as in other model systems. However, activation of mTOR is also dependent of kinases other than AKT. Here, we show that activation of mTOR is not dependent on AKT in a prostate-specific PTEN-deficient mouse model of prostate cancer. Pathway bifurcation of AKT and mTOR was noted in both mouse and human prostate tumors. We demonstrated for the first time that cotargeting mTOR and AKT with ridaforolimus/MK-8669 and M1K-2206, respectively, delivers additive antitumor effects in vivo when compared to single agents. Our preclinical data suggest that the combination of AKT and mTOR inhibitors might be more effective in treating prostate cancer patients than current treatment regimens or either treatment alone.

A peptidoglycan monomer with the glutamine to serine change and basic peptides bind in silico to TLR-2 (403-455).

Bacterial cell wall polysaccharides, such as PGN, bind and activate TLR-2, NOD2 and PGRP on monocytes/macrophages and activate inflammation. We found that the peptides containing basic amino acids (cations) at N -terminus and tyrosine at C-terminus interfered with activating ability of PGN. This finding is significant because the ECD of TLR-2 in vivo encounters a large number of proteins or peptides. Some should bind ECD and "pre-form" TLR-2 to respond or not to its activators, although they cannot activate TLR-2 alone. TLR-2 is receptor for a large number of ligands, including lipopeptides and bacterial cell wall glycoproteins. A binding site for lipopeptides has been identified; however, a binding site for soluble or multimeric PGN has not been proposed. To identify the candidate binding sites of peptides and PGN on TLR-2, we modeled docking of peptides and of the PGN monomer (PGN-S-monomer) to extracellular domain (ECD-TLR-2) of the unbound TLR-2. Quantification, in silico, of free energy of binding (DG) identified 2 close sites for peptides and PGN. The PGN-S-monomer binding site is between amino acids TLR-2, 404-430 or more closely TLR-2, 417-428. The peptide-binding site is between amino acids TLR-2, 434-455. Molecular models show PGN-S-monomer inserts its N -acetyl-glucosamine (NAG) deep in the TLR-2 coil, while its terminal lysine interacts with inside (Glu(403)) and outside pocket (Tyr(378)). Peptides insert their two N -terminal arginines or their C-terminal tyrosines in the TLR-2 coil. PGN did not bind the lipopeptide-binding site in the TLR-2. It can bind the C-terminus, 572-586 (DG = 0.026 kcal), of "lipopeptide-bound" TLR-2. An additional, low-affinity PGN-binding site is TLR-2 (227-237). MTP, MDP, and lysine-less PGN bind to TLR-2, 87-113. This is the first report identifying candidate binding sites of monomer PGN and peptides on TLR-2. Experimental verification of our findings is needed to create synthetic adjuvant for vaccines. Such synthetic PGN can direct both adjuvant and cancer antigen to TLR-2.

Downregulation of Notch pathway by a gamma-secretase inhibitor attenuates AKT/mammalian target of rapamycin signaling and glucose uptake in an ERBB2 transgenic breast cancer model.

ERBB2/neu and Notch signaling are known to be deregulated in many human cancers. However, pathway cross-talk and dependencies are not well understood. In this study, we use an ERBB2-transgenic mouse model of breast cancer (neuT) to show that Notch signaling plays a critical role in tumor maintenance. Inhibition of the Notch pathway with a gamma-secretase inhibitor (GSI) decreased both the Notch and the mammalian target of rapamycin/AKT pathways. Antitumor activity resulting from GSI treatment was associated with decreased cell proliferation as measured by Ki67 and decreased expression of glucose transporter Glut1. Positron emission tomography (PET) imaging showed that the functional consequences of decreased Glut1 translated to reduced glucose uptake and correlated with antitumor effects as measured by micro-computed tomography imaging. The decrease of Glut1 in neuT tumors was also observed in several human breast cancer cell lines following GSI treatment. We provide evidence that approximately 27% of ERBB2-positive human breast cancer specimens display high expression of HES1, phospho-S6RP, and GLUT1. Together, these results suggest that pathways downstream of Notch signaling are, at least in part, responsible for promoting tumor growth in neuT and also active in both neuT and a subset of human breast cancers. These findings suggest that GSI may provide therapeutic benefit to a subset of ERBB2-positive breast cancers and that [(18)F]FDG-PET imaging may be useful in monitoring clinical response.

Inhibition of tumor growth progression by antiandrogens and mTOR inhibitor in a Pten-deficient mouse model of prostate cancer.

Androgen receptors have been shown to play a critical role in prostate cancer. We used ultrasound imaging techniques to track tumor response to antiandrogen and rapamycin treatment in a prostate-specific Pten-deleted mouse model of cancer. Depletion of androgens by either surgical or chemical castration significantly inhibited tumor growth progression without altering the activation of Akt and mammalian target of rapamycin (mTOR). We also showed for the first time that targeting mTOR along with antiandrogen treatment exhibited additive antitumor effects in vivo when compared with single agents. Our preclinical data suggest that combination of antiandrogens with mTOR inhibitors might be more effective in treating androgen-dependent prostate cancer patients.

Taxol increases the amount and T cell activating ability of self-immune stimulatory multimolecular complexes found in ovarian cancer cells.

It has been proposed that chemotherapy enhances tumor antigen (TA)-specific immunity. The molecular form of TA from ovarian tumor that activates cellular immunity is unknown. We report here identification of a novel molecular form of immunogenic TA for CD8(+) cells named self-immune stimulatory multimolecular complexes (ISMMC). ISMMC consist of a molecular complex of polyosome/ribosome-bound ubiquitinated nascent HER-2 polypeptides. This complex is chaperoned by heat shock protein Gp96, which mediates ISMMC uptake by antigen-presenting cells through the scavenger receptor CD91. RNAs in ISMMC stimulate immature dendritic cells to secrete interleukin 12 and induce IFN-gamma in peripheral blood mononuclear cells. ISMMC dissociate, retrotranslocate from the lysosome to cytoplasm, and are processed to peptides by the proteasome. At subpharmacologic doses, Taxol increased the amount of ISMMC by three to four times and modified their composition by inducing the attachment of cochaperones of HSP70, such as the mitotic-phase phosphoprotein 11J. On a total protein basis, Taxol induced ISMMC, expanded more CD8(+) cells, activated more CD56(+) NKG2D(+) cells to produce IFN-gamma, and were more potent inducers of high T-cell receptor density Perforin(+) cells than native ISMMC and peptide E75. Elucidation of the composition of ISMMC and identification of adducts formed by Taxol should be important for developing molecular cancer vaccines.

Novel natural immunogenic peptides from Numb1 and Notch1 proteins for CD8+ cells in ovarian ascites.

Notch is a plasma membrane receptor involved in the control of cell fate specification and in the maintenance of the balance between proliferation and differentiation in many cell lineages. Disruption of Notch has been implicated in a variety of hematological and solid cancers. Numb is also expressed in many adult mammalian cells. Adult cells divide symmetrically, and Numb is symmetrically partitioned at mitosis. The Numb-mediated regulation of Notch is believed to play a causative role in naturally occurring breast cancers. Reduction of Numb levels in breast tumors is regulated by proteasomal degradation. We reasoned that if the disregulated negative control of Notch by Numb protein is the consequence of Numb proteasomal degradation, then degradation of Numb can generate peptides which are transported, presented by MHC-I molecules. Surprisingly we found few candidate naturally processed peptides from Notch1, Notch2, and Numb1. CD8+ T cells expressing TCRs which specifically recognized peptides Notch1 (2112-2120) and Numb1 (87-95) were presented in the ascites of ovarian cancer patients. Many of these cells were differentiated and expressed high levels of Perforin. The natural immunogenicity of Notch1 and particularly of Numb1 suggests a mechanism of immunosurveillance which is overcome during tumor progression. Immunotherapy with tumor antigens from Notch and Numb should be important for treatment of cancer patients.

Mitogen stimulation activates different signaling pathways in early- and late-divided T cells as revealed by cDNA microarray analysis.

Mobilization of tumor-reactive CD8+ T cells remains the major challenge of cancer immunotherapy. Knowing how and when the T cell response expands and differentiates after antigen stimulation would make a significant contribution to the development of tumor vaccines. In the current study, we used CFSE-based cell sorting and cDNA microarray to identify the gene expression profile of adjacent generations of T cells after PHA stimulation. Early-divided generations of T cells responded to stimulation by activating cell cycle and surviving gene pathways, while late generations of T cells had more dramatic changes in transcription of cytokine genes. Reconstruction of biochemical pathways, activated in both early and late generations of T cells, also confirmed the impact of division in focal-adhesion kinases. Because most tumors are infiltrated by lymphocytes, our studies indicate a novel approach to identify 'systemic biological responses' of T cells, which could determine the design, and optimization of effective tumor vaccines.

Prostate tumor cells infected with a recombinant influenza virus expressing a truncated NS1 protein activate cytolytic CD8+ cells to recognize noninfected tumor cells.

Many viral oncolytic approaches against cancer are based on the ability of specific viruses to replicate in tumors expressing components of the constitutively activated Ras/mitogen-activated protein kinase (MAPK) pathways and/or inhibited or dysregulated alpha/beta interferon (IFN-alpha/beta) response pathways. A major issue when considering these approaches is their applicability to tumors that lack activated Ras. To identify the effector mechanisms activated by oncolytic viruses, we investigated inhibition of proliferation of the prostate cancer line LNCap by the recombinant TR-NS1 influenza A virus, a genetically attenuated influenza A/PR8/34 virus expressing a truncated nonstructural protein (NS1) of 126 amino acids. LNCap cells lack constitutively activated MAPK, extracellular signal-regulated kinase (ERK), and p38 and are resistant to death by IFN-alpha. Truncation of the NS1 protein of influenza viruses is known to result in viral attenuation due to a reduced ability of the NS1 to inhibit the IFN-alpha/beta response. Infection with TR-NS1 virus rapidly activated ERK-1 more than ERK-2 in LNCap cells. Importantly, TR-NS1 virus infection transiently inhibited cell proliferation and induced apoptosis in LNCap cells. Addition of peripheral blood mononuclear cells (PBMC) and interleukin 12 (IL-12) to TR-NS1 virus-infected LNCap cells (TR-NS1-LNCap) resulted in faster elimination of TR-NS1-LNCap cells compared with LNCap cells. Moreover, TR-NS1-LNCap cells induced IFN-gamma in PBMC. The levels of IFN-gamma were amplified by IL-12. TR-NS1-LNCap cells also induced tumor-lytic cytotoxic T lymphocytes (CTL). These CTL lysed noninfected LNCap cells in a CD8-dependent manner. Activation of cellular immunity to tumor cells by viruses is an intriguing effector pathway, which should be especially significant for elimination of human tumors that lack activated Ras.

Synthetic microRNA and double-stranded RNA targeting the 3'-untranslated region of HER-2/neu mRNA inhibit HER-2 protein expression in ovarian cancer cells.

MicroRNA (miRNA) are a class of non-coding RNAs found both in normal tissues and cancer cells. The natural miRNA, which target cancer genes for transcriptional repression are still unknown. Approaches for synthetic miRNA design targeting cancer genes have not yet been established. We designed miRNAs targeting the 3' UTR (nt 4350-4372) of HER-2 proto-oncogene. One miRNA (miR-14U) was designed by introducing a mutation in the nt 14 counting from the 5' end of anti-sense RNA. Two others (miR4350-10GGA and miR4350-11AAGCU) were designed by introducing either loop-forming nucleotides in position 10 or a part of the complementary sequence of the Brd-box consensus sequence, in position 11. miR4350-10GGA was more effective than the anti-sense strand in decreasing the numbers of ovarian tumor SKOV3 cells, which over-expressed HER-2 protein. Its inhibitory effects were lower than that of corresponding double-stranded (ds) RNA4350-4372. Inhibition of HER-2 expression mediated by miRNAs was higher in cells expressing higher levels of HER-2 protein than in cells expressing lower levels of HER-2 protein. This is the first demonstration of inhibition of expression of a constitutively over-expressed tumor protein by designed synthetic miRNA and its cor-responding dsRNA targeting 3' untranslated regions in mRNA. Our results also show that measuring the effects of miRNA and dsRNA in pooled populations of tumor cells, which express various levels of target oncogenes, may reflect the survival responses of siRNA resistant tumors rather than the growth inhibitory responses of siRNA-sensitive tumors.

Stimulation of human T cells by an influenza A vector expressing a CTL epitope from the HER-2/neu protooncogene results in higher numbers of antigen-specific TCRhi cells than stimulation with peptide. Divergent roles of IL-2 and IL-15.

Development of cancer vaccines requires approaches to induce expansion and functional differentiation of tumor antigen-specific effector and memory cells. The later are particularly relevant for prevention of disease relapse. Efficient induction of memory cells is hindered by the lack of information about the relationship between TCR stimulation and the cytokines required for Ag-specific memory CD8+ cells and proliferation and survival. Since viruses are known to induce memory T cells, an attenuated influenza A/PR8/34 virus with a truncated nonstructural (NS1) gene was generated containing the HER-2 CTL E75 epitope in its neuraminidase protein (KIF-NS virus). Stimulation of PBMC from healthy donors and of tumor-associated lymphocytes (TAL) from ovarian cancer patients with dendritic cells (DC) infected with KIF-NS (KIF-NS-DC), induced higher numbers of immediate memory effector CD8+ CD44hi CD122hi cells, expressing TCR specific for E75 (E75-TCR) than stimulation with peptide E75. Survival of CD44hi CD122hi cells was dependent on the levels of TCR; cells expressing lower levels of E75-TCR (MFI: 10(2)-10(3)) survived better in IL-2 while cells expressing high levels of TCR (MFI: 10(3)-10(4)) survived better in IL-15. This is the first report demonstrating induction of human Ag-specific memory CD8+ cells against a human tumor-antigen using a live attenuated recombinant influenza virus vector. Such vectors may provide a novel approach for preventive immunity in human cancer vaccine development.

Sensitivity of undifferentiated, high-TCR density CD8+ cells to methylene groups appended to tumor antigen determines their differentiation or death.

CD8(+) cells expressing high numbers of TCR per cell (TCR(hi)) are considered important mediators of antitumor effects. To understand the relationship between TCR density and antigen affinity for TCR in the outcome of stimulation with antigen and differentiation of CTL recognizing tumor antigen, we analyzed perforin induction in ovarian tumor-associated lymphocytes in response to the smallest possible changes in the atomic forces of interaction between antigen and TCR. Stimulating undifferentiated, apoptosis-resistant CD8(+) cells expressing high levels of E75-TCR (TCR(hi)) with variants of the CTL epitope E75, HER-2 (369-377), induced their stepwise differentiation, first to IFN-gamma(+) Perf(-) and to TCR(hi) IFN-gamma(+) Perf(+) cells. Blocking caspase-9 activation at antigen stimulation also enhanced the generation of TCR(hi) Perf(hi) cells, demonstrating that TCR density dictated the pathway of death activated by stimulation with the same agonist. Expansion and differentiation of TCR(hi) Perf(+) CTL required an agonist of optimal CH(2) side chain length, which in this study was equal to two CH(2) groups appended to E75 at the Gly(4) position. Side chains one CH(2) shorter or longer than optimal were either less stimulatory or induced death of TCR(hi) Perf(+) cells. Differentiation of TCR(hi) CD8(+) cells can be finely tuned by synthetic amino acids in the peptide, whose side chains induce small increments in the affinity of the antigen for TCR below the affinity which induce apoptosis.

Fine specificity of high molecular weight-melanoma-associated antigen-specific cytotoxic T lymphocytes elicited by anti-idiotypic monoclonal antibodies in patients with melanoma.

HLA-A2-restricted CTLs, which lysed high molecular weight (HMW)-melanoma-associated antigen (MAA)(+) melanoma cells, were induced in patients with melanoma immunized with MELIMMUNE, a combination of the murine anti-idiotypic (anti-id) monoclonal antibodies (mAb) MEL-2 and MF11-30 (MW Pride et al., Clin Cancer Res 1998;4:2363.). In the present study we investigated whether CTL epitopes are present in anti-id mAb MF-11-30 and activate T cells to recognize HMW-MAA on melanoma cells. One candidate epitope in the mAb MF11-30 VH chain, VH (3-11), was selected based on the presence of HLA-A2 anchor residues and partial homology with the HMW-MAA epitope, HMW-MAA (76-84). Lymphocytes from HLA-A2(+)-immunized patients proliferated to VH (3-11) peptide and to a variant HMW-MAA peptide to a significantly greater extent than autologous lymphocytes stimulated with an irrelevant peptide and lymphocytes from nonimmunized patients. No proliferative response was detected to the wild-type HMW-MAA peptide (76-84). Significant increase in IFN-gamma production but not in interleukin 10 production in response to VH (3-11) and to variant HMW-MAA peptide (76-84) was observed in lymphocytes from the immunized patients. Stimulation of lymphocytes from HLA-A2(+) patients with the two peptides induced CTL, which lysed HMW-MAA(+)/HLA-A2(+) A375SM melanoma cells. This is the first report documenting the presence of immunogenic peptides in a murine anti-id mAb for a defined epitope expressed by a human melanoma-associated antigen. These results may be relevant for development of novel vaccines based on homology between anti-id mAb and tumor-associated antigen amino acid sequences.

Stimulation of cells from a non-invaded and an invaded lymph node with a HER-2+ tumor with peptides corresponding to T-cell epitopes E75 and G89 induced expansion of central memory cells (TCM) from the metastasis-negative lymph nodes.

Breast cancer metastasizes from the primary site to the axillary lymph nodes (LN). It is unknown whether tumor metastasis abolishes or enhances the ability of LN cells to develop a specific response to the Ag expressed by the tumor, and whether an immune response to the same Ag is present in the tumor-free LN. We stimulated lymphocytes from a metastasis negative (Met-) and a metastasis positive (Met+) LN, invaded by a HER-2+ tumor, from the same patient, with HER-2 peptides E75 (369-377) and G89 (776-778). E75 define a CTL epitope presented by HLA-A2, while G89 define a CD4+ cell recognized epitope. Met- LN responded to E75+G89 with higher expansion of E75 TCR+ CD45RO+ CCR7- (CCR7-) and E75-TCR+ CD45RO+ CCR7+ (CCR7+) cells than Met+ LN. Stimulation with E75+G89 induced a significant increase in CCR7+ cells in Met- LN compared with Met+ LN. The levels of IFN-alpha and IL-15 were higher in Met- LN cultures stimulated with E75+G89 than in Met+ LN cultures. This increase did not correlate with the levels of induction of IFN-gamma, IL-4, and IL-10. The finding of higher expansion of Ag specific CCR7+ cells and of differentiation to CCR7- cells, which define the TCM and TEM subsets respectively, in Met- LN, by G89 is novel for tumor systems. This may have implications for preventative vaccination strategies for breast and ovarian cancer.

Clinical studies of vaccines targeting breast cancer.

Many clinical studies have been undertaken to assess the therapeutic potential of vaccination and have included a large variety of cancer immunogens. Most of these studies involved patients with metastatic cancer, which is characterized by the most aggressive malignant cells, the longest-lasting disease, and the failure of all standard cytotoxic treatments. The presence of tumor over long periods and the toxicity of previous treatments tend to negatively affect immune responsiveness to tumor antigens presented by the vaccine. In this review, we analyze the ability of past and current vaccine therapies to induce clinical responses in breast cancer. To date, clinical responses have been observed by using vaccines targeting HER-2/neu protein, human telomerase reverse transcriptase, carcinoembryonic antigen, and carbohydrate antigen given after stem cell rescue. The review concludes with a discussion of possible future directions for vaccine development and applications.

Activation of tumor antigen-specific cytotoxic T lymphocytes (CTLs) by human dendritic cells infected with an attenuated influenza A virus expressing a CTL epitope derived from the HER-2/neu proto-oncogene.

The development of cancer vaccines requires approaches to induce expansion and functional differentiation of tumor antigen-specific cytotoxic T lymphocyte (CTL) effectors which posses cytolytic capability and produce cytokines. Efficient induction of such cells is hindered by the poor immunogenicity of tumor antigens and by the poor transduction efficiency of dendritic cells (DCs) with current nonreplicating vectors. We have investigated the use of influenza A virus, a potent viral inducer of CTLs, as a vector expressing the immunodominant HER-2 CTL epitope KIF (E75). For this purpose, an attenuated influenza A/PR8/34 virus with a truncated nonstructural (NS1) gene was generated containing the E75 epitope in its neuraminidase protein (KIF-NS virus). Stimulation of peripheral blood mononuclear cells from healthy donors and of tumor-associated lymphocytes from ovarian and breast cancer patients with DCs infected with KIF-NS virus (KIF-NS DC) induced CTLs that specifically recognized the peptide KIF and HER-2-expressing tumors in cytotoxicity assays and secreted gamma interferon (IFN-gamma) and interleukin-2 at recall with peptide. Priming with KIF-NS DCs increased the number of E75(+) CD45RO(+) cells by more than 10-fold compared to nonstimulated cells. In addition, KIF-NS virus induced high levels of IFN-alpha in DCs. This is the first report demonstrating induction of human epitope-specific CTLs against a tumor-associated antigen with a live attenuated recombinant influenza virus vector. Such vectors may provide a novel approach for tumor antigen delivery, lymphocyte activation, and differentiation in human cancer vaccine development.

Induction of tumor-reactive CTL by C-side chain variants of the CTL epitope HER-2/neu protooncogene (369-377) selected by molecular modeling of the peptide: HLA-A2 complex.

To design side chain variants for modulation of immunogenicity, we modeled the complex of the HLA-A2 molecule with an immunodominant peptide, E75, from the HER-2/neu protooncogene protein recognized by CTL. We identified the side chain orientation of E75. We modified E75 at the central Ser(5) (E75 wild-type), which points upward, by removing successively the HO (variant S5A) and the CH2-OH (variant S5G). Replacement of the OH with an aminopropyl (CH2)3-NH3 (variant S5K) maintained a similar upward orientation of the side chain. S5A and S5G were stronger stimulators while S5K was a weaker stimulator than E75 for induction of lytic function, indicating that the OH group and its extension hindered TCR activation. S5K-CTL survived longer than did CTL induced by E75 and the variants S5A and S5G, which became apoptotic after restimulation with the inducer. S5K-CTL also recognized E75 endogenously presented by the tumor by IFN-gamma production and specific cytolysis. S5K-CTL expanded at stimulation with E75 or with E75 plus agonistic anti-Fas mAb. Compared with S5K-CTL that had been restimulated with the inducer S5K, S5K-CTL stimulated with wild-type E75 expressed higher levels of E75(+) TCR and BCL-2. Activation of human tumor-reactive CTL by weaker agonists than the nominal Ag, followed by expansion with the nominal Ag, is a novel approach to antitumor CTL development. Fine tuning of activation of tumor-reactive CTL by weak agonists, designed by molecular modeling, may circumvent cell death or tolerization induced by tumor Ag, and thus, may provide a novel approach to the rational design of human cancer vaccines.

Helper peptide G89 (HER-2:777-789) and G89-activated cells regulate the survival of effectors induced by the CTL epitope E75 (HER-2, 369-377). Correlation with the IFN-gamma: IL-10 balance.

The CTL response to Ag expands after priming and subsequently contracts reducing the number of effectors. CD4+ cells are described as regulators of CTL immunity. To elucidate whether CD4+ cells are involved in survival of effector CTL and the survival signals, we used CTL and Th peptides form the HER-2 protooncogene recognized in association with HL-A2 and HLA-DR4, respectively. We analyzed the effect of cells stimulated with G89 (777-789) in survival and expression of lytic function of CTL specific for the epitope E75 (369-377). G89 primed cells (G89-PR) and G89 enhanced expansion and Ag-specific cytolyis of CTL at priming with E75, but inhibited survival of E75-specific CTL at restimulation. These effects were not simply a reflection of the increases in IFN-gamma and IL-10, but the ratio IFN-gamma/lL-10 modified by G89 differentially regulated the survival of stimulated cells. This suggests that the use of helper antigens in cancer vaccines should be evaluated in the context of their CTL survival inducing effect.

Treatment with HER-2 phosphorylation agonists enhance tumor ability to stimulate epitope specific CTL in vitro.

The transmembrane (TM) receptor encoded by the HER-2 proto-oncogene (HER-2) is amplified in several types of human carcinomas and premalignant states and provides an important target for cancer therapy. While overexpression of HER-2 should lead to increased CTL epitope formation due to the attendant increase in higher protein turnover, breast tumors are poor stimulators of CTL. In this report, we show that treatment of SKBR3.A2 tumor cells with HER-2 receptor agonists (EGF and NDF) enhanced tumor ability to activate CTL from tumor associated lymphocytes (TAL) and from T cells from peripheral blood in vitro. The enhanced ability of tumor cells to stimulate CTL was paralleled by tyrosine phosphorylation of HER-2, and its oligo-ubiquitination compared with control untreated, or TPA-treated tumor cells. Our results demonstrate that HER-2 ligands used at concentrations which induce tyrosine phosphorylation but not downregulation of the receptor can be used to enhance the ability of tumor cells to activate CTL. This may have implications for overcoming Ag ignorance and tolerance in human cancers.