Cryptic Peptides-Based Vaccines for Breast Tumor Treatment

Institution: Sidney Kimmel Cancer Center
Investigator(s): Joseph Lustgarten, Ph.D. -
Award Cycle: 2003 (Cycle IX) Grant #: 9WB-0100 Award: $371,110
Award Type: STEP Award
Research Priorities
Detection, Prognosis and Treatment>Innovative Treatment Modalities: search for a cure



Initial Award Abstract (2003)
Her-2/neu protein is found to be in more than 35% of all breast cancers. Her-2/neu expression has been associated with metastatic disease, poor prognosis and low survival, as such this protein represents an excellent target for immunotherapy. The immune system normally does not attack the body’s own tissues or proteins. Considering that Her-2/neu is a protein found naturally in the body (a self-protein), attempts to develop vaccines targeting the Her-2/neu are often disappointing because the immune responses against Her-2/neu are very weak and ineffective for tumor elimination or growth control. The challenge is to identify a system where vaccines can induce strong immune responses against Her-2/neu to cause tumor rejection.

Our goal is develop a vaccine strategy that will induce the generation of potent immune responses capable of eliminating Her-2/neu positive tumors. Our strategy is to identify a series of small molecules (cryptic peptides) that mimic or resemble the Her-2/neu. Since these small molecules are not self-proteins we will be able to induce strong immune responses that will recognize Her-2/neu positive tumors and eliminate them. We have already identified some small molecules that effectively recognize Her-2/neu tumors. Our objective is to test these small molecules (cryptic peptides) as cancer vaccines.

We used a new chemical methodology called positional scanning synthetic peptide combinatorial library (PS-SCL) to identify small molecules recognize by T cells (T cells are part of the immune system that help to clear out infections and malignancies such cancer). By screening the chemical libraries of small molecules (peptides) with T cells specific for Her-2/neu that we have developed previously, we were able to identify some small molecules recognized by these T cells. We used a mouse model to test whether these small molecules induce a T cell response in vivo. Our results demonstrate that these small molecules induce a T cell response and these T cells kill Her-2/neu breast tumors with high efficiency. These results demonstrated that these small molecules are effective inducers of immune responses. We will use our mouse tumor model to test these small molecules as cancer vaccines. We will inoculate mice with tumor cells, vaccinate them with the small molecules and then evaluated the vaccine for tumor protection.

Currently there are no effective vaccines for the treatment of Her-2/neu breast tumors. The studies proposed here will allow us to test for the first time if the small molecules (cryptic peptides) we have identified are good candidates for cancer vaccines. Importantly, these small molecules can be used in humans for the treatment of breast cancer. As such, these peptides could be of great clinical value and the information gain from these studies could form the basis for future studies in the clinic.


Final Report (2006)
T cells that target proteins that are normally found in the body are deleted during the developmental process of the immune system to avoid damage to self-tissues. However, this process, called T-cell tolerance, handicaps immune responses against tumor antigens since many of these antigens are also present in normal tissues. One of the consequences of such tolerance is that T cells with a strong attraction to the tumor protein (high avidity) are deleted leaving only those with at weak attraction.

We have initiated studies to assess the strength of T cells against Her-2/neu using the Her-2/neu transgenic mice (neu mice) in which the rat Her-2/neu is under the control of the MMTV promoter. The neu mice were crossed with A2.1/Kb mice (A2xneu), and T cell specific responses against the p369-377 and p773-782 A2.1-Her-2/neu restricted peptides were evaluated. Our preliminary data confirmed that the cytotoxic T-cell lymphocytes (CTLs) from miceA2xneu mice, which had the Her-2/neu in their genomes, were of a much lower avidity for the peptides than the CTLs from A2.1/KbxFVB-wild type mice (A2xFVB). Studies in cancer patients show that responses to these epitopes are also of relatively low avidity. Thus, attempts to expand these responses may be of little clinical value. However, immune responses with higher avidity can be evoked from crossreactive epitopes.

We hypothesized that if not all possible crossreactive peptides are naturally processed and presented, then T cells against these crossreactive peptides may persist in the repertoire and can be used to induce stronger antitumor responses against native epitopes present on the tumor cells. We have used the positional scanning synthetic peptide combinatorial library (PS-SCL) methodology to screen the p369-377 and p773-782 T cell clones. We have identified potential amino acids that can be substituted in the primary sequences of these peptides. More importantly, we have identified crossreactive peptides designed for the p773-782 peptide that induce CTL responses of relatively high affinity in A2xneu mice, and these CTLs recognize A2+-Her-2/neu+ tumors with high efficiency.

These results demonstrated that it was possible to circumvent tolerance with the identification of crossreactive peptides and that these peptides could be of significant clinical value. Furthermore, preliminary results demonstrated that these small molecules induce an antitumor response that substantially inhibited the tumor growth when compared to the original peptide, indicating that these small molecules can serve as cancer vaccines. These results are extremely encouraging in that small molecules that mimic the original peptide can be used as a new strategy to develop more efficient vaccines.


Symposium Abstract (2005)
T cell tolerance handicaps the immune responses against tumor antigens since many of these antigens are also expressed in non- transformed tissues. One of the consequences of such tolerance is that high avidity T cells for the tumor antigen are deleted leaving only a low avidity repertoire. We have initiated studies to assess the T cell repertoire against Her-2/neu using the Her-2/neu transgenic mice (neu mice). The neu mice were crossed with A2.1/Kb mice (A2xneu) and T cell specific responses against the p773-782 A2.1-Her-2/neu restricted peptides were evaluated. Our preliminary data confirmed that the CTLs from A2xneu mice of a much lower avidity for the peptides as compared to the CTL from A2.1/KbxFVB-wild type mice (A2xFVB). Thus, attempts to expand these responses may be of little clinical value. However, immune responses with higher avidity can be evoked from crossreactive epitopes (also called heteroclitic analogs).

We hypothesized that if not all possible crossreactive peptides are naturally processed and presented, the possibility exists that T cells against these crossreactive peptides persist in the repertoire and can be used to induce stronger antitumor responses against native epitopes present on the tumor cells. We have used the positional scanning synthetic peptide combinatorial library (PS-SCL) to screen the p773-782 T cell clones.. We have identified crossreactive peptides derived from the PS-SCL screening that are recognized by p773-782 T-cell clones. These peptides induce CTL responses of relatively high affinity in A2xneu mice. Furthermore, these CTLs recognize A2+-Her-2/neu+ tumors with high efficiency. Immunization of A2xneu with the crossreactive peptides significantly retards the tumor growth in these mice. Taken together, these results demonstrated that it was possible to circumvent tolerance with the identification of crossreactive peptides and that these peptides could be of significant clinical value.