Michael J. Heffernan, Ph.D.
Department of Pediatrics, Section of Tropical Medicine
The Drug and Vaccine Delivery Laboratory conducts research on drug delivery systems for vaccines, cancer therapies, and other biomedical applications. In the area of vaccine delivery, we are developing microparticle-based adjuvant systems for recombinant protein- and DNA-based vaccines. Other drug delivery applications include targeted nanoparticle delivery of cancer chemotherapeutics and nanoparticle delivery of antibody therapeutics.
Adjuvant/delivery systems for subunit vaccines against tropical diseases
There is an urgent need for new treatment strategies for neglected tropical diseases (NTDs). In many cases, vaccination is considered to be the most cost-effective approach. Our group is currently focusing on developing recombinant protein subunit vaccines against Chagas disease and leishmaniasis. Chagas disease is caused by infection with the parasite Trypanosoma cruzi, with an estimated 8-9 million persons infected, primarily in the Latin American and Caribbean (LAC) region. Cutaneous leishmaniasis is a disease marked by skin sores that is caused by parasites of the Leishmania genus, which are endemic in 88 countries. Current therapies for Chagas disease and leishmaniasis often are cost-prohibitive, have low efficacy, and have significant adverse side effects.
One key technical hurdle is the development of adjuvant systems for protein subunit vaccines. Purified recombinant protein antigens are weakly immunogenic, and traditional adjuvants based on aluminum compounds typically elicit Th2-type (antibody) responses. However, treatment of intracellular parasitic infections, such as Chagas disease and leishmaniasis, will require the induction of Th1-type cellular immune responses, which are characterized by the generation of IFNg-secreting CD4 T cells and cytotoxic CD8 T cells. Therefore, we are developing microparticle-based delivery systems to deliver recombinant protein antigens and immunostimulatory adjuvant molecules to antigen-presenting cells in vivo, in order to control the Th1/Th2 polarization of the immune response. The adjuvant molecules are typically Toll-Like Receptor (TLR) agonists, such as CpG oligodeoxynucleotide (TLR9), imiquimod (TLR7), or Eisai E6020 adjuvant (TLR4). The recombinant proteins and adjuvants are loaded into poly(lactic-co-glycolic) acid (PLGA) microspheres using oil/water emulsion, solvent evaporation methods. We collaborate closely with Dr. Bin Zhan’s group in the Sabin-TCH vaccine center, who express and purify recombinant protein antigens for the tropical disease vaccines.
We evaluate the immunogenicity of the microparticle vaccine formulations in mice, by giving subcutaneous injections of the vaccine (prime and boost), and after 2-4 weeks, analyzing the serum antibodies and splenocytes. We typically evaluate the recall response of splenocytes to re-stimulation with protein antigen, by measuring CD4 and CD8 T cell proliferation and secretion of cytokines by T cells. Vaccination studies with PLGA microparticles containing ovalbumin (OVA) and CpG-ODN have demonstrated an antigen-specific, Th1-polarized immune response, with an increase in splenocyte IFN-g secretion and IgG2b antibody levels, as compared to PLGA[OVA], soluble OVA+CpG, or Alum[OVA]. Ongoing and future studies include measuring immunogenicity of microparticles with T. cruzi or L. donovani protein antigen and testing the efficacy of the microparticle vaccines at preventing or treating parasite infections using T. cruzi and Leishmania challenge models in mice.
Adjuvant/delivery system for DNA vaccine against ureaplasma infection
We are collaborating with Dr. Leonard Weisman in the Department of Pediatrics, Section of Newborn Medicine, on developing a microparticle-based DNA vaccine against ureaplasma, a bacterial infection that is associated with adverse pregnancy outcomes and neonatal diseases. Ureaplasma bacterial infection of the upper genital tract can induce host inflammatory responses that lead to preterm labor and neonatal lung injury, including bronchopulmonary dysplasia (BPD). While antibiotics are used for treating maternal and neonatal Ureaplasma infections, they do not appear to be effective in reducing the incidence of preterm birth or BPD. Recent studies in the Weisman laboratory have shown that a plasmid DNA (pDNA) vaccine encoding for the Ureaplasma multiple-banded antigen (MBA) generates strong antibody responses and reduces adverse pregnancy outcomes in mouse models. DNA vaccines, however, have in general required optimization of adjuvant/delivery systems and genetic constructs in order to be translated to humans. In this project, we are developing an adjuvant/delivery system for a Ureaplasma DNA vaccine, in order to improve transfection efficiencies of the pDNA antigen and to co-deliver immunostimulatory adjuvants. In vivo immunogenicity testing has shown an increase in antibody response when the pDNA is encapsulated in PLGA microparticles and co-administered with microparticles containing CpG-ODN. Future work will include testing the efficacy of the microparticle/DNA vaccine in a mouse model of ureaplasma infection.
Targeted nanoparticles for delivery of cancer therapeutics
In collaboration with Dr. Qizhi (Cathy) Yao in the Department of Surgery, we are developing a mesothelin-targeted nanoparticle for the delivery of gemcitabine to treat pancreatic cancer. The nanoparticles are designed to bind to mesothelin, a protein that is overexpressed in several types of cancers, including pancreatic cancer, but has relatively little expression in normal tissues. We hypothesize that mesothelin-targeted nanoparticles will enhance the accumulation of gemcitabine in the tumor, to promote tumor regression while reducing adverse systemic effects. The PLGA nanoparticles are coated with an anti-mesothelin antibody single-chain variable fragment (MSLN-scFv), which is expressed as a recombinant protein by Dr. Bin Zhan’s group. We expect that incorporation of the MSLN-scFv antibody fragment will result in equal or better targeting in comparison to the whole monoclonal antibody, and in addition the recombinant protein method is viewed as a favorable for production. We have produced MSLN-scFV coated nanoparticles with sizes of 100 to 300 nm diameter, and we have observed greater binding of the targeted nanoparticles to MSLN-expressing cells than negative control cells, using fluorescent microscopy. Ongoing work is focused on quantifying relative binding to different cell types, loading gemcitabine into the nanoparticles, and demonstrating cytotoxic effects of the gemcitabine-loaded nanoparticles.
Intravitreal delivery of bevacizumab (Avastin®) to treat retinopathy of prematurity (ROP)
We are also developing a nanoparticle system for intravitreal delivery of antibody therapeutics for treating retinopathy of prematurity (ROP), in collaboration with Dr. Lingkun Kong in the Section of Newborn Medicine. The monoclonal anti-VEGF antibody, bevacizumab (Avastin®), is being used to treat ocular diseases; however, it has a short intravitreal half-life, on the order of 3 to 5 days, which limits its therpeutic effect. In addition, when used to treat retinopathy in premature infants, there is a concern that even a moderate amount of transport of bevacizumab into the bloodstream can be detrimental. We have hypothesized that delivery of bevacizumab on the surface of PLGA nanoparticles would result in greater retention of the drug in the vitreous humor and would significantly reduce the amount of drug in the bloodstream. We have prepared bevacizumab-coated PLGA nanoparticles with sizes of 150 to 200 nm diameter. Preliminary testing in adult mice indicates that intravitreal injection of bevacizumab-nanoparticles results in substantially lower bloodstream levels of the drug when compared to injection of free drug. Ongoing work will include pharmacokinetics studies and testing in ROP disease models in mice.
Section of Pediatric Tropical Medicine
Department of Pediatrics
Baylor College of Medicine
Feigin Center, Room C.0550.10
1102 Bates Street
Houston, Texas 77030
B.S., Duke University, 1990
M.S., Virginia Polytechnic Institute, 1995
Ph.D., Georgia Institute of Technology, 2008
Postdoctoral, National Cancer Institute, Bethesda, Maryland, 2008-2011
1. Hotez PJ, Dumonteil E, Heffernan MJ, Bottazzi ME. Innovation for “the bottom 100 million”: Eliminating neglected tropical diseases in the Americas through mass drug administration and new vaccines for hookworm and Chagas disease. Advances in Experimental Medicine and Biology: Hot Topics in Infection and Immunity in Children IX. Curtis, Nigel; Finn, Adam; Pollard, Andrew J. (Eds.), Springer, 2013.
2. Eric Dumonteil E, Bottazzi ME, Zhan B, Heffernan MJ, et al. Accelerating the Development of a Therapeutic Vaccine for Human Chagas Disease: Rationale and Prospects. Expert Review of Vaccines 2012;11(9):1043-1055.
3. Zaharoff, D. A., Heffernan, M., Fallon, J. and Greiner, J. W. (2012) Preclinical and Clinical Use of Chitosan and Derivatives for Biopharmaceuticals: From Preclinical Research to the Bedside, in Chitosan-Based Systems for Biopharmaceuticals: Delivery, Targeting and Polymer Therapeutics (eds B. Sarmento and J. das Neves), John Wiley & Sons, Ltd, Chichester, UK. doi: 10.1002/9781119962977.ch27
4. Heffernan MJ, Zaharoff DA, Fallon JK, Schlom J, Greiner JW. In vivo efficacy of a chitosan/IL-12 adjuvant system for protein-based vaccines. Biomaterials 2011;32(3):926-932. PMCID: PMC2992965.
5. Heffernan MJ, Murthy N. Disulfide-crosslinked polyion micelles for delivery of protein therapeutics. Annals of Biomedical Engineering 2009;37(10):1993-2002.
6. Heffernan MJ, Kasturi SP, Yang SC, Pulendran B, Murthy N. The stimulation of CD8+ T cells by dendritic cells pulsed with polyketal microparticles containing ion-paired protein antigen and poly(inosinic acid)-poly(cytidylic acid). Biomaterials 2009;30(5):910-918.
7. Lee S, Yang SC, Heffernan MJ, Taylor WR, Murthy N. Polyketal microparticles: a new delivery vehicle for superoxide dismutase. Bioconjugate Chemistry 2007;18(1):4-7.
8. Heffernan MJ, Murthy N. Polyketal nanoparticles: a new pH-sensitive biodegradable drug delivery vehicle. Bioconjugate Chemistry 2005;16(6):1340-1342.
Meagan Barry (MD/PhD, TBMM)