HeLa cells are an immortalized cell line, meaning they can divide and grow indefinitely in a laboratory setting. Unlike most human cells, which have a limited lifespan outside the body, HeLa cells provide a consistent and abundant supply for research purposes. This characteristic makes them valuable for various scientific studies.
The Accidental Discovery
The origin of HeLa cells traces back to February 8, 1951, when Henrietta Lacks, a 31-year-old African American woman, sought treatment for cervical cancer at Johns Hopkins Hospital in Baltimore, Maryland. During a biopsy of her aggressive tumor, tissue samples were collected without her knowledge or consent, a practice that was common at the time. These samples were then transferred to the tissue culture laboratory of Dr. George Gey at Johns Hopkins.
Dr. Gey had attempted for years to establish a continuously growing human cell line, but previous patient samples only survived for days. However, cells from Henrietta Lacks’ tumor behaved differently, showing a remarkable ability to survive and proliferate rapidly. These cells, later named HeLa after Henrietta Lacks, doubled approximately every 20 to 24 hours. This unique characteristic marked the accidental discovery of the first “immortal” human cell line, setting the stage for advancements in biomedical research.
The Genetic Transformation
The remarkable immortality of HeLa cells stems from a rare combination of biological events, primarily involving infection with human papillomavirus (HPV) and the subsequent activation of an enzyme called telomerase. Henrietta Lacks’ cervical cells were infected with HPV-18, a high-risk strain of the virus known for its carcinogenic potential. The viral DNA from HPV-18 integrated into the host cell’s genome, specifically at sites that disrupted certain tumor suppressor genes.
Two viral oncoproteins, E6 and E7, produced by the integrated HPV DNA, played a significant role in this transformation. The E6 protein targets and promotes the degradation of the p53 tumor suppressor protein, which normally regulates cell division and initiates programmed cell death. Simultaneously, the E7 protein binds to and inactivates the retinoblastoma (Rb) family of tumor suppressor proteins, which control cell cycle progression by inhibiting cell division. By neutralizing these tumor suppressors, E6 and E7 allowed the infected cells to bypass normal cellular checkpoints and proliferate uncontrollably.
Beyond the disruption of tumor suppressor pathways, HeLa cells also exhibit active telomerase, an enzyme not typically active in most mature human somatic cells. Normal cells have protective caps on their chromosomes called telomeres, which shorten with each cell division, eventually limiting cell proliferation. In HeLa cells, however, HPV infection and other genetic changes activated telomerase. This enzyme continuously rebuilds and maintains telomeres, preventing their shortening and allowing the cells to divide indefinitely. This combination of viral disruption and telomere maintenance was a rare occurrence, leading to this cell line’s creation.
Unlocking Medical Breakthroughs
The perpetual growth and division of HeLa cells in a laboratory setting made them an invaluable tool, enabling repeatable experiments. Their robust nature allowed scientists to maintain consistent cell populations for extended periods. This consistent supply of identical human cells proved instrumental in developing the polio vaccine in the 1950s, as researchers could culture large quantities of the poliovirus in HeLa cells to understand its infection mechanism and test vaccine efficacy.
HeLa cells have also contributed significantly to cancer research, providing a model to study the disease’s mechanisms and test potential treatments. They were used to explore the effects of radiation and toxins on human cells, contributing to our understanding of cellular responses to various environmental factors. HeLa cells played a role in gene mapping, aiding the Human Genome Project, and have been utilized in research concerning AIDS, leukemia, and other diseases. Their application extends to space biology, where they have been used to investigate the effects of microgravity on human cells. Their ability to divide indefinitely made them a foundation for many experiments, accelerating discoveries across diverse fields of medical research.