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Visualization of effective tumor targeting by CD8+ natural killer T cells redirected with bispecific antibody
Christian Scheffold1, Martin Kornacker, Yolanda C Scheffold
1Division of Bone Marrow Transplantation, Stanford University School of Medicine, California 94305, USA.
Abstract:
HER2 is an attractive immunotherapeutic target for neoplastic disease because this cell surface molecule is overexpressed on a large fraction of malignant tumor cells. To directly assess therapeutic responses to targeted therapy by noninvasive in vivo imaging in small animals, human HER2-expressing ovarian carcinoma cells were genetically modified with a firefly luciferase gene, and light emission was used for visualization of tumor growth and response to therapy. This imaging approach was able to demonstrate in real-time tumor regression in a HER2 xenograft mouse model by adoptive transfer of in vitro induced and expanded cytotoxic CD8+ natural killer T (NKT) cells retargeted with a humanized bispecific antibody F(ab')(2)HER2xCD3. Immunotherapy with effector cells alone or a humanized monoclonal antibody anti-p185(HER2) (4D5-8) resulted in significant but slower reduction in tumor burden. Long-term survival of tumor xenografts correlated inversely with visible residual tumor burden. In vitro, F(ab')(2)HER2xCD3 substantially augmented cytotoxic activity of CD8+ NKT cells. By flow-sorting, CD8+ NKT cells coexpressing CD56 were found to have the highest redirected killing ability. Treatment with concanamycin A or EGTA abrogated CD8+ NKT cytotoxicity indicating that perforin is a major pathway of tumor cell lysis. In contrast, when CD8+ NKT cell were cross-linked with F(ab')(2)HER2xCD3 neither the immunosuppressants cyclosporine A and FK506, nor the increase of intracellular cyclic AMP by dibutyryl cyclic AMP were able to inhibit cytotoxicity demonstrating that signaling via the CD3 antigen changes the biological activity of non-MHC-restricted effector cells. These studies have demonstrated that CD8+ NKT cells can be successfully redirected to tumor cells using bispecific antibodies and offer a promising strategy for adoptive immunotherapy of neoplastic diseases.
Insights
This study shows that bispecific antibodies can redirect cytotoxic CD8+ natural killer T (NKT) cells to target HER2-expressing cancer cells. This approach enables real-time imaging of tumor regression, offering a promising strategy for adoptive cancer immunotherapy.
Area of Science:
- Immunology
- Oncology
- Biotechnology
Background:
- HER2 is a cell surface molecule overexpressed in many cancers, making it a prime target for immunotherapy.
- Noninvasive in vivo imaging is crucial for assessing therapeutic responses to targeted cancer therapies.
Purpose of the Study:
- To evaluate the efficacy of retargeted cytotoxic CD8+ natural killer T (NKT) cells using a bispecific antibody for HER2-positive ovarian cancer therapy.
- To visualize and assess tumor regression in real-time using bioluminescence imaging.
Main Methods:
- Genetically modified human HER2-expressing ovarian carcinoma cells with a firefly luciferase gene for imaging.
- Adoptive transfer of in vitro expanded CD8+ NKT cells retargeted with a bispecific antibody (F(ab')(2)HER2xCD3) in a HER2 xenograft mouse model.
- Compared efficacy with effector cells alone and a monoclonal antibody (4D5-8).
Main Results:
- Real-time visualization of tumor regression was achieved using the imaging approach.
- Bispecific antibody-mediated retargeting of CD8+ NKT cells led to significant tumor regression.
- CD8+ NKT cells expressing CD56 showed the highest redirected killing ability, primarily via the perforin pathway.
- Cytotoxicity was resistant to common immunosuppressants, indicating altered effector cell activity.
Conclusions:
- CD8+ NKT cells can be effectively redirected to tumor cells using bispecific antibodies.
- This strategy represents a promising approach for adoptive immunotherapy of neoplastic diseases.
- Noninvasive imaging facilitates real-time monitoring of therapeutic responses.