To add the Control :
CheckBox cb=new CheckBox();
cb.ID="myCb";
gv.Rows[0].Cells[0].Controls.add(cb);
to remove the checkbox:
CheckBox cb=new CheckBox();
cb=gv.Rows[0].Cells[0].FindControl("myCon") as CheckBox;
gv.Rows[0].Cells[0].Controls.Remove((Control)cb);