HeLa


 * for other meanings, see also the disambiguation page Hela

A HeLa cell (also Hela or hela cell) is an immortal cell line used in medical research. The cell line was derived from cervical cancer cells taken from Henrietta Lacks, who died from her cancer in 1951.

George Otto Gey and Henrietta Lacks
The cells were propagated by George Otto Gey without Lacks' knowledge or permission and later commercialized, although never patented in their original form. There was then, as now, no requirement to inform a patient, or their relatives, about such matters because discarded material, or material obtained during surgery, diagnosis or therapy was the property of the physician and/or medical institution. This issue and Ms. Lacks' situation was brought up in the Supreme Court of California case of John Moore v. the Regents of the University of California. The court ruled that a person's discarded tissue and cells are not their property and can be commercialized.

Initially, the cell line was said to be named after a "Helen Lane" or "Helen Larson", in order to preserve Lacks's anonymity. Despite this attempt, her real name was used by the press within a few years of her death. These cells are treated as cancer cells, as they are descended from a biopsy taken from a visible lesion on the cervix as part of Ms. Lacks' diagnosis of cancer, but a debate still continues on the classification of the cells.

HeLa cells are termed "immortal" in that they can divide an unlimited number of times in a laboratory cell culture plate as long as basic cell survival conditions are met (i.e. being maintained and sustained in a suitable environment). There are many strains of HeLa cells as they continue to evolve by being grown in cell cultures, but all HeLa cells are descended from the same tumor cells removed from Ms. Lacks. It has been estimated that the total mass of HeLa cells that have been propogated in cell culture far exceeds the number of cells in Henrietta Lacks' body.

Telomerase
The HeLa cell line was derived for use in cancer research. These cells proliferate abnormally rapidly, even compared to other cancer cells. HeLa cells have an active version of the enzyme telomerase during cell division, which prevents the incremental shortening of telomeres that is implicated in aging and eventual cell death. In this way, HeLa cells circumvent the Hayflick Limit, which is the limited number of cell divisions that most normal cells can undergo before dying out in cell culture.

Chromosome number
Horizontal gene transfer from human papillomavirus 18 (HPV18) to human cervical cells created the HeLa genome which is different from either parent genome in various ways including its number of chromosomes. HeLa cells have a modal chromosome number of 82, with four copies of chromosome 12 and three copies of chromosomes 6, 8, and 17.

Human papillomaviruses (HPVs) are frequently integrated into the cellular DNA in cervical cancers. We mapped by FISH five HPV18 integration sites: three on normal chromosomes 8 at 8q24 and two on derivative chromosomes, der(5)t(5;22;8)(q11;q11q13;q24) and der(22)t(8;22)(q24;q13), which have chromosome 8q24 material. An 8q24 copy number increase was detected by CGH. Dual-color FISH with a c-MYC probe mapping to 8q24 revealed colocalization with HPV18 at all integration sites, indicating that dispersion and amplification of the c-MYC gene sequences occurred after and was most likely triggered by the viral insertion at a single integration site. Numerical and structural chromosomal aberrations identified by SKY, genomic imbalances detected by CGH, as well as FISH localization of HPV18 integration at the c-MYC locus in HeLa cells are common and representative for advanced stage cervical cell carcinomas. The HeLa genome has been remarkably stable after years of continuous cultivation; therefore, the genetic alterations detected may have been present in the primary tumor and reflect events that are relevant to the development of cervical cancer.

Contamination
Because of their avid adaptation to growth in tissue culture plates, HeLa cells are sometimes difficult to control. For example, they have proven to be a persistent laboratory "weed" and they can contaminate other cell cultures in the same laboratory, interfering with biological research. The degree of HeLa cell contamination among other cell types is unknown, because few researchers test the identity or purity of already-established cell lines. It has been demonstrated that a substantial fraction of in vitro cell lines - approximately 10%, maybe 20%, are actually HeLa cells, due to the fact that the original cells in the cell culture have been overwhelmed by a rapidly growing population derived from HeLa contaminant cells. Stanley Gartler in 1967 and Walter Nelson-Rees in 1975 were the first to publish on the contamination of various cell lines by HeLa.

Helacyton gartleri
Due to their ability to replicate indefinitely, and their non-human number of chromosomes, Leigh Van Valen described HeLa as an example of the contemporary creation of a new species, Helacyton gartleri, named after Stanley M. Gartler, who Van Valen credits with discovering "the remarkable success of this species". His argument for speciation depends on three points: As well as proposing a new species for HeLa cells, Van Valen proposes in the same paper that the new family Helacytidae and the genus Helacyton.
 * The chromosomal incompatibility of HeLa cells with humans.
 * The ecological niche of HeLa cells.
 * Their ability to persist and expand well beyond the desires of human cultivators.