Altering the combination and order of variable and constant domains is highly likely to have an impact on the propensity for stabilisation of the CH1 domain, resulting in subversion of the ER quality control system. contribute to the heterogeneity of antibody species secreted during the expression of therapeutic antibodies. This subversion of the normal quality control process is dependent on the HC variable domain, is prevalent with CEP-18770 (Delanzomib) engineered antibodies and can occur when only the Fab fragments are expressed. This discovery will have an impact on the efficient production of both humanised antibodies and the design of novel antibody formats. Keywords:antibodies, antibody folding, antibody production, antibody secretion, endoplasmic reticulum == Introduction == The ability to humanise rodent antibodies efficiently along with improvements in recombinant expression has led to the development of several high-value and effective therapeutics [1]. However, efforts to produce novel antibody formats such as bi- or tri-specific molecules have met with difficulties in terms of low titres and poor yields, resulting in longer production runs and the requirement for extensive purification [2]. Rabbit Polyclonal to RAD17 The heterogeneity in expressed protein is likely to be caused by a lack of efficient folding and assembly of the desired antibody and the subsequent secretion of alternate assemblies. Given the potential for antibodies and their derivatives as therapeutics, any improvements in optimising the production process in terms CEP-18770 (Delanzomib) of yield and quality will have an impact on their utility and affordability. The correct folding and assembly of antibodies requires an elegant cellular quality control process [3]. Crucially, heavy chains (HCs) are retained in the cell as dimeric intermediates until two light chains (LCs) assemble with the HC dimer to form a tetramer, which is then released from this retention and secreted from the cell [4]. The HC dimer is retained due to a lack of folding of the CH1 domain in the absence of the cognate LC, resulting in a high-affinity interaction with the intracellular chaperone, immunoglobulin HC-binding protein (BiP) [5,6]. This interaction is reversed upon LC assembly with the CLdomain acting as a template to allow correct folding of the CH1 domain [7,8]. This cellular mechanism ensures that only correctly folded and assembled molecules are secreted from an antibody-producing cell. The quality control system also functions in Chinese hamster ovary (CHO) cells used for commercial antibody production with BiP retaining unassembled HC dimers [9]. However, the fidelity of this retention has not been analysed for engineered antibodies as it has been assumed that the retention is efficient, at least during the expression of commonly expressed IgG formats. While the retention mechanism seems to hold for many natural antibodies, HC dimers can be secreted in LC-deficient mice if they lack the CH1 domain [6,10]. Camelids also express HCs that lack a CH1 domain, allowing the secretion of functional HC dimers [11]. In addition, some transcripts found in mammalian pro-B-cells encode HCs that can be expressed on the cell surface in the absence of any surrogate or conventional LC [12]. These HCs contain a CH1 domain, which folds in the absence of a LC, enabling them to escape the endoplasmic reticulum (ER) quality control mechanism. Interestingly, these HCs are not found in pre- or mature B-cells, indicating the presence of a negative selection for cells expressing HCs that can be secreted in the absence of a LC. Importantly, these HCs differ only in their variable domain, indicating that the requirement for LC-dependent folding of the CH1 domain is an intrinsic property of the VHdomain that is selected for during B-cell development. In the present study, we show that some engineered HCs can also be secreted as dimers. The CH1 domain within these HC constructs can fold in the absence of the cognate LC, thereby subverting the cellular quality control process. The results suggest that the humanisation process can inadvertently create HC constructs that would normally be selected against during B-cell development. == Experimental procedures CEP-18770 (Delanzomib) == == Cell lines and DNA constructs == CHO adherent cells (CHO) L761H were grown in Dulbecco’s Modified Eagle Medium (DMEM) containing 10% foetal calf serum. CHO-S suspension cells (Life Technologies) were grown in CD CHO chemically defined medium. All HCs contained either the human IgG1 or IgG4 CH1,2,3 domains fused to either mouse or humanised VHdomains with specificity for A33 [13], TNF- [14], CD20 [15], CD25 (Zenapax) [16], CD25 (Simulect) [17] and CD11a [18]. The variable domain from.
