Alexandra L. Howell, PhD
Professor of Medicine
Professor of Microbiology and Immunology
Research Biologist, Veterans Affairs Medical Center (White River Junction, VT)
Microbiology and Immunology
University of Texas Graduate School of Biomedical Sciences, Ph.D., 1982
Colby College, BA, 1977
Program in Experimental and Molecular Medicine
VA Medical Center
Research Service, Box 151
215 North Main St.
White River Jct. VT 05009
Office: Building 44-VA Hospital
Use of CRISPR/Cas to cleave the integrate HIV proviral sequence in primary macrophages and lymphocytes
Analysis of off-target cleavage events in human cells
Development of novel Cas enzymes (CasX, CasY)
Use of humanized mouse models to study anti-HIV therapeutics
Research projects in Dr. Howell's laboratory are focused on developing viral and non-viral vectors to deliver the CRISPR/Cas guide RNA and Cas genes to HIV infected cells as well as to uninfected cells to provide protection from infection. Analysis of both on-target as well as off-target cleavage events are determined by Circle-Seq and Guide-Seq methodologies. We are developing novel Cas enzymes (Cas12d and Cas12e) from newly identified bacterial species that show advantages over the use of Cas9.
Our previous work focused on mechanisms to block HIV-1 infection in mucosal tissue sites, specifically the female reproductive tract. These experimental model systems included the study of RNA interference to block expression of host cell receptors used by HIV-1 for infection (CD4 and CCR5), as well as a novel humanized mouse that possesses a human immune system. This humanized mouse model system can be infected with HIV-1 intravenously and also at mucosal sites including the reproductive and gastrointestinal tracts, and has been successfully used to model human infection.
Rotations and Thesis Projects
1. Determine optimal conditions for the transduction of human cells with AAV vectors expressing CRISPR/Cas genes.
2. Develop novel Cas enzymes and guide RNA to target the hepatitis B virus (HBV), both the integrated and covalently closed circular DNA versions of the HBV genome.
3. Assess efficacy of viral and non-viral delivery mechanisms for CRISPR/Cas genes to liver and bone marrow in humanized mice models.
Merit Review from the VA (2021-2024)
SBIR Phase I grant- NIH (2020)
Dr. Howell has mentored several PEMM graduate students in her laboratory, both through rotations and for their thesis. In addition, she has mentored Dartmouth undergraduate senior thesis scholars.
Dr. Howell received her B.A. from Colby College in 1977, and her Ph.D. from the University of Texas Graduate School of Biomedical Sciences, Houston, TX, in 1982. After postdoctoral work as a research fellow and research associate in the department of Microbiology/Immunology at Dartmouth Medical School, Dr. Howell joined the faculty of the Departments of Microbiology/Immunology and Medicine at Dartmouth Medical School in 1984. She moved to the VA Medical Center in 1989 to develop an HIV core facility and has been funded by the VA since 1993 to support studies in HIV.
CAS12e (CASX2) CLEAVAGE OF CCR5: IMPACT OF GUIDE RNA LENGTH AND PAM SEQUENCE ON CLEAVAGE ACTIVITY.
Attitudes of Virginia Dentists Toward Dental Therapists: A pilot study.
The intrinsic neonatal hippocampal network: rsfMRI findings.
Analysis of CRISPR/Cas9 Guide RNA Efficiency and Specificity Against Genetically Diverse HIV-1 Isolates.
A mathematical model of HIV dynamics treated with a population of gene-edited haematopoietic progenitor cells exhibiting threshold phenomenon.
Toll-like receptor agonists are potent inhibitors of human immunodeficiency virus-type 1 replication in peripheral blood mononuclear cells.
Gardiquimod: a Toll-like receptor-7 agonist that inhibits HIV type 1 infection of human macrophages and activated T cells.
Breast milk from Tanzanian women has divergent effects on cell-free and cell-associated HIV-1 infection in vitro.
Nanoparticles containing siRNA to silence CD4 and CCR5 reduce expression of these receptors and inhibit HIV-1 infection in human female reproductive tract tissue explants.
Human uterine natural killer cells but not blood natural killer cells inhibit human immunodeficiency virus type 1 infection by secretion of CXCL12.