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Open Access Communication

Effective Delivery of Cancer Vaccines with Oxidatively Photo-Inactivated Transgenic Leishmania for Tumor Immunotherapy in Mouse Models

Kwang Poo Chang 1,*, Dennis K. P. Ng 2, Chia-Kwung Fan 3, Ramesh B. Batchu 4, Bala K. Kolli 1

  1. Department of Microbiology/Immunology, Center for Cancer cell Biology, Immunology and Infection, Chicago Medical School/Rosalindfranklin University of Medicine and Science, 3333 Green Bay Rd, N Chicago, IL 60064, USA

  2. Department of Chemistry, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong

  3. Department of Molecular Parasitology and Tropical Diseases, College of Medicine, Taipei Medical University, 250 Wu-Xing Street, Taipei, Taiwan

  4. Division of Surgical Oncology & Developmental, Therapeutics, The Michael and Marian Ilitch Department of Surgery, Wayne State University, 4646 John R Road, Detroit, MI 48201, USA

Correspondence: Kwang Poo Chang

Academic Editor: Tapan K Bera

Special Issue: Molecular Cancer Therapeutics

Received: December 29, 2019 | Accepted: February 21, 2020 | Published: February 24, 2020

OBM Genetics 2020, Volume 4, Issue 1, doi:10.21926/obm.genet.2001103

Recommended citation:Chang KP, Ng DKP, Fan CK, Batchu RB, Kolli BK. Effective Delivery of Cancer Vaccines with Oxidatively Photo-Inactivated Transgenic Leishmania for Tumor Immunotherapy in Mouse Models. OBM Genetics 2020; 4(1): 103; doi:10.21926/obm.genet.2001103.

© 2020 by the authors. This is an open access article distributed under the conditions of the Creative Commons by Attribution License, which permits unrestricted use, distribution, and reproduction in any medium or format, provided the original work is correctly cited.


The parasitic protozoa in the genus of Leishmania have exceptionally favorable attributes for exploitation as a vehicle for safe and effective delivery of transgenically incorporated vaccines against infectious and malignant diseases. A dual suicidal mechanism was installed in Leishmania via genetic and chemical engineering in vitro for accumulation of photosensitizers, rendering them sensitive to dim light for inactivation. Leishmania so inactivated are non-viable, but immunologically competent to deliver vaccines for immune-prophylaxis and –therapy. We have begun to explore the utility of these Leishmania for immunization against tumors in experimental mouse models.


Leishmania; transgenics; photodyanmic inactivation; vaccine delivery; immunotherapy; tumor

Antigen-specific vaccination remains to be an option for tumor immunotherapy. Delivery of vaccines for this approach includes the strategies of using attenuated bacterial and viral constructs, e.g. Listeria [1,2] and Vaccinia [3]. Leishmania are parasitic protozoa, which are uniquely favorable for use as a universal platform to deliver vaccines for disease prevention and therapy [4,5]. Of particular interest are human cutaneous Leishmania, which causes innocuous, self-resolving skin infection [6]. Life-long immunity develops after its spontaneous cure, indicative of not only the presence of Leishmania-specific vaccine molecules against leishmaniasis but also adjuvanticity critical for effective vaccination against this and other diseases, e.g. malignancy. Leishmania are equipped with eukaryotic translational machineries and post-translational mechanisms for correct expression of multiple transgenic vaccines in abundance, thereby enabling them to serve as a carrier of high efficiency. Additionally, Leishmania are endowed with multifarious molecules to protect endogenous vaccines and target them specifically to antigen presenting cells (APC), i.e. dendritic cells (DC) and macrophages – the exclusive host cells for the residence of these parasites in natural infection. Attributable to these vaccine-protection and APC-homing properties are their surface lipoglycoconjugates, contributing to Leishmania adjuvanticity for effective vaccination. Leishmania are intrinsically safe. They produce no toxins [7,8] and show no human toxicity when used extensively after chemical or physical inactivation of whole cells in Leishmanin skin test for delayed type hypersensitivity and in several large scale vaccine trial attempts [6].

We have developed novel strategies to completely inactivate Leishmania to ascertain their safety with the preservation of its adjuvanticity as a vaccine carrier, viz. their genetic and chemical engineering in vitro to install light-activated duo suicidal mechanisms. This is made possible by partial genetic complementation of their deficiencies in heme biosynthetic enzymes for cytosolic accumulation of UV-sensitive uroporphyrin [9,10] and by loading of their endosomes exogenously with red-light sensitive cationic phthalocyanine [11,12,13]. Brief illumination of these photo-sensitized Leishmania results in their rapid oxidative inactivation initiated by the generation of extremely short-lived, albeit highly destructive singlet oxygen [14]. The safety and efficacy of such inactivated Leishmania have been demonstrated by immunization of animals, producing neither infection nor adverse effects [15], but prophylactically protect them against both cutaneous and visceral leishmaniasis [16,17], and immunotherapeutic activities clinically against drug-incurable canine leishmaniasis [18]. Moreover, Leishmania transgenically made to express ovalbumin (OVA) was shown to effectively deliver this antigen, after photodynamic inactivation, to DC for processing and presentation to activate OVA epitope-specific T cells in vitro [12]. Human cancer vaccine candidates have been successfully expressed in transgenic Leishmania, including enolase 1 (hENO1) [19]. These inactivated Leishmania produced impressive activities of immunotherapy by suppressing the emergence of tumors, which were pre-established with murine and human lung cancer cells in mice [20]. In one model, frozen samples of photo-inactivated Leishmania were used and found more effective than CpG ODN as adjuvants for immunizations with recombinant ENO1 peptides against murine tumor. In another, photo-inactivated hENO1-expressing Leishmania were used alone for immunizations of BALB/c mice followed by adaptive transfer of immunity via their splenic cells to immunocompromised mice bearing human tumor. Work is under way to assess such photodynamic vaccination in another murine model for pancreatic cancer. Of interest is to study the mechanism of adjuvanticity of photo-inactivated Leishmania in detail for comparison with other DAMP and PAMP adjuvants. Tumor antigens have been delivered to patients’ DC via conjugation with cell-penetrating peptides [21] and adeno-associated virus vectors [22] for ex vivo vaccination to activate CD8+ T cells for CTL activities of anti-tumor immunity. Such protocols are being developed for use with inactivated hENO1-Leishmania toward DC-based immunotherapy of human lung cancer.


Thanks are due to many colleagues for their indispensable collaboration and to the support of NIH-NIAID Grant # AI-68835, AI-7712375, AI097830 to KPC for the development of photodynamically inactivated Leishmania as vaccines and vaccine carriers.

Author Contributions

Conceptualization & writing, KP Chang; Funding Acquisition & Supervision, KP Chang, DKP Ng, RB Bachu, CK Fan; Methodology & Investigation, BK Kolli, RB Bachu, DKP Ng.

Competing Interests

The authors have declared that no competing interests exist.


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