1472 Ad-ISF35- Transduced Autologous Cells Promote In Vitro and In Vivo Chemosensitization to FCR and Durable Complete Responses In Patients with Del(17p) / P53 Defective Chronic Lymphocytic Leukemia

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Blank1472 Ad-ISF35- Transduced Autologous Cells Promote In Vitro and In Vivo

Chemosensitization to FCR and Durable Complete Responses In Patients with

Del(17p) / P53 Defective Chronic Lymphocytic Leukemia

Oral and Poster Abstracts

Poster Session: Gene Therapy and Transfer: Poster I

Saturday, December 4, 2010, 5:30 PM-7:30 PM

Hall A3/A4 (Orange County Convention Center)

Poster Board I-452

Januario E Castro, M.D1*, Johanna Melo-Cardenas, B.Sc1*, Sebastian

Barajas-Gamboa, M.D1*, Mauricio Urquiza, PhD1*, Mark J. Cantwell, PhD2* and

J. Kipps, MD, PhD3

1Division of Hematology and Oncology, s-UCSD Cancer Center, University of

California, San Diego, San Diego, CA, UCSD, La Jolla, CA

2Memgen, LLC,, Dallas, TX

3The University of California, San Diego, La Jolla, CA

Background: Chronic lymphocytic leukemia (CLL) cells with del(17p) typically

have loss of functional P53, rendering them refractory to chemotherapeutic

agents. However, del(17p) CLL cells activated by CD40L (CD154) are induced to

express pro-apoptotic factors that re-sensitize cells to the cytotoxic activity

of P53-dependent drugs, such as fludarabine (F-ara-A). Chemotherapy

re-sensitization is mediated in part by induction of p73, a p53-related

transcription factor. To examine whether a CD154-based therapeutic strategy can

be developed in vivo for del(17p) and/or fludarabine refractory CLL, a phase 1b

clinical study evaluating an autologous cellular gene immunotherapy is being

conducted. Autologous CLL cells transduced ex vivo with a replication defective

adenovirus vector encoding a membrane-stable, re-engineered form of CD154

(Ad-ISF35) are administered, followed by standard courses of FCR in subjects

with high-risk fludarabine refractory and/or del(17p) CLL.

Methods: Subjects with fludarabine refractory and/or del(17p) receive three IV

doses (one dose every two weeks) of 3x108 autologous CLL cells that have been

transduced ex vivo with Ad-ISF35. Two weeks following the third dose of

Ad-ISF35-transduced cells, subjects receive standard monthly cycles of

fludarabine, cyclophosphamide and rituximab (FCR). Study endpoints include

analysis of safety and efficacy. Correlative analyses are conducted for

evidence of drug re-sensitization, regulation of apoptotic pathways, cytokine

analysis, and humoral immune responses to the adenovirus vector and ISF35

transgene.

Results: To date, four patients have completed treatment. Two patients have

achieved a compete response, one of them without detectable minimal residual

disease (MRD) by sensitive multiparameter flow cytometry of marrow mononuclear

cells after completion of treatment. These responses have been durable after a

median follow up of 18 months. One patient achieved a partial response with

complete resolution of lymphocytosis, lymphadenopathy and splenomegaly, but

residual CLL in the bone marrow. The remaining patient had progressive disease

despite an initial response to both infusion of Ad-ISF35-transduced cells and

FCR chemoimmunotherapy. Infusion of Ad-ISF35 transduced cells has been well

tolerated. Overall, the most common adverse events have been transient fever,

malaise and fatigue associated with infusion of Ad-ISF35-transduced cells and

cytopenias after treatment with FCR. Prior to ISF35 treatment, CLL cells from

patients were resistant to F-ara-A induced apoptosis (IC50 > 10µM). However,

one day following the first infusion of Ad-ISF35-transduced CLL cells, patient

cells became sensitive to F-ara-A (IC50 0.3-1 µM). In addition, pro-apoptotic

factors, including Bid, DR5, CD95, and P73 were induced in the non-transduced

“bystander” CLL population following ISF35 infusion. These pro-apoptotic

effects persisted = 2 weeks following IV infusion. The sera from treated

patients showed increase in IL-6 and IFN-? after infusion of Ad-ISF35 transduced

CLL cells. Despite evidence of anti-adenovirus antibody responses in the treated

patients, there was no detectable anti-human CD154 production before or after

ISF35 treatment.

Conclusions: The results indicate that Ad-ISF35-cell-gene therapy can sensitize

P53-deficient CLL to “P53-dependent” cytotoxic agents in vivo, allowing for

effective and durable clinical responses. These data are very encouraging and

suggest that this unique chemoimmunotherapy re-sensitization strategy could

offer a valuable treatment option for patients who otherwise would be resistant

to standard forms of therapy.