Requirement of cell lines: For the maintenance of Cell line some basic conditions are required. These are described as follows.

1. pH: Most cell lines grow well at pH 7.4. Although the optimum pH for cell growth varies relatively little among different cell strains, some normal fibroblast lines perform best at pH 7.4 to pH 7.7, and transformed cells may do better at pH 7.0 to pH 7.4.

2.  Buffering: Culture media must be buffered under two sets of conditions:

1. Open dishes, where the evolution of CO₂ causes the pH to rise
2. Overproduction of CO₂ and lactic acid in transformed cell lines at high cell concentrations, when the pH will fall.

3.  Temperature: The temperature recommended for most human and warm-blooded animal cell lines is 37°C, closely to body heat, but generally set a little lower for safety, because overheating may become major problem than under heating.

4.  Media: Although many cell lines are still propagated in medium supplemented with serum, in many instances cultures may now be propagated in serum-free media. Media that have been produced commercially will have been tested for their capability of sustaining the growth of one or more cell lines. However under certain circumstance we can use our own media.

5.  Growth curve: A growth curve gives three parameters of measurement: (1) the lag phase before cell proliferation is initiated after subculture, indicating whether the cells are having to adapt to different conditions; (2) the doubling time in the middle of the exponential growth phase, indicating the growth promoting capacity of the medium; and (3) the maximum cell concentration attainable indicating whether there are limiting concentrations of certain nutrients. In cell lines whose growth is not sensitive to density (e.g., continuous cell lines), the terminal cell density indicates the total yield possible and usually reflects the total amino acid or glucose concentration.

Generation of cell lines: Stably transfected cell lines are used extensively in drug discovery. Cell lines expresses a target of interest, such as a G-protein coupled receptor (GPCR) or a reporter gene, form the basis for most cell-based compound screening campaigns. In establishing new assays for high throughput screening, creation of the appropriate cell line is a bottleneck. Typically, a stable cell line is created by transfection with a plasmid encoding the target of interest or reporter gene construct, and an additional gene which allows for chemical selection of successfully transfected cells (usually an antibiotic resistance gene). Through a lengthy selection process and subsequent limiting dilution to obtain clones, the desired stable cell line is generated. This process takes approximately 2-3 months, usually yielding 5-10 usable clones and allowing little control over the end result throughout the process.

Technique for cell line generation:

LEAP (Laser-Enabled Analysis and Processing) has been developed for high-throughput laser-mediated cell elimination for cell purification. It is a precise laser-based cell ablation enables cell purification based on fluorescent and morphological criteria. It has whole well imaging system i.e all cells in the well can be analysed. It has F-theta scanning optics i.e Image up to 40X faster than typical HCS (High-content screening) systems. Image magnifications of 3X, 5X, 10X, or 20X can be obtained. Combinations of 8 excitation and 8 emission wavelengths is possible. LEAP images all cells within a well, selects a specific population of cells by gating, and eliminates selected cells at >10³ per second. LEAP can select cells of interest based on fluorescent properties, morphological properties, or a combination of both. By replacing the antibiotic resistance gene used for chemical selection with a gene encoding a fluorescent protein, transfected cells can be selected based on fluorescence. These cells can then be purified using LEAP by specifically eliminating non-fluorescent cells using laser elimination. By selecting cells that remain fluorescent and proliferate over a period of time, stable cell lines are isolated. In addition, fluorescence level may be used to identify cell lines with a specific desired expression level of the transfected construct. The fluorescent reporter gene may also be replaced by a variety of fluorescent cell physiology read outs, enabling the selection of cells based on functional responses.