70% are in suspension as clumps. This indicates two problems

One is incomplete digestion so that the cells form clumps. To have a complete trypsinization, use 2-3 ml of Trypsin-EDTA (0.25%), 5 min in 37 ^o C for digestion.

Another one is incomplete removal of trypsin after digestion. So the cells cannot attach back to the surface of the cultureware

It is suggested to centrifuge the digested cell solution in 100xg or 1000rpm (eppendorf benchtop centrifuge) for 5min. Aspirate off the trypsin solution and wash the cell pellet with PBS twice and plate it in new culture flask.

 According to this article, 

Tanizaki Y, Kobayashi A, Toujima S, Shiro M, Mizoguchi M, Mabuchi Y, Yagi S, Minami S, Takikawa O, Ino K. Indoleamine 2, 3‐dioxygenase promotes peritoneal metastasis of ovarian cancer by inducing an immunosuppressive environment. Cancer science. 2014 Aug 1;105(8):966-73.

it mentioned,

"Cell lines and culture. A mouse ovarian carcinoma cell line,OV2944-HM-1, derived from B6C3F1 mice (pairings of C57BL ⁄ 69 C3H ⁄ HeN), was purchased from Riken BRC Cell Bank (Tsukuba, Japan). HM-1 cells were cultured in MEMalpha (Life Technologies, Carlsbad, CA, USA) supplemented with 10% FCS (Sigma-Aldrich) and penicillin–streptomycin– amphotericin B (Life Technologies)."

Establishment of stable IDO-overexpressing transfectants.

The expression vector for mouse IDO was constructed by inserting full-size mouse IDO cDNA(22) into pcDNA3.1 (Invitrogen, Carlsbad, CA, USA). Transfection into HM-1 cells was carried out as described previously.(21) More than 20 stable clones were selected as IDO-overexpressing cells (HM-1-IDO). For a negative control, the control vector was transfected into HM-1 cells (HM-1-mock). HM-1-IDO cells and IDO-mock cells were cultured using G418 (Sigma-Aldrich) at 200 lg ⁄mL in MEMalpha supplemented with 10% FCS."

For reference 21, 

Yoshida N, Ino K, Ishida Y et al. Overexpression of indoleamine 2,3-dioxygenase

in human endometrial carcinoma cells induces rapid tumor growth in

a mouse xenograft model. Clin Cancer Res 2008; 14: 7251–9.

The mammalian expression vector for human IDO (pcDNA3.1-IDO) was constructed by inserting full-size human IDO cDNA (21) between the KpnI and XbaI sites of pcDNA3.1 (Invitrogen). Transfection into AMEC cells was carried out using Lipofectamine 2000 according to the manufacturer’s instructions (Invitrogen). Stable transfectants were selected by growth in medium supplemented with 400 Ag/mL G418 (Sigma-Aldrich), and more than 20 clones resistant to G418 were obtained as IDO-overexpressing cells (AMEC-IDO). For negative control experiments, the pcDNA3.1 vector without inserted IDO cDNA was transfected into AMEC cells (AMECpcDNA)."

So, without any specific precaution, this cell probably is an adherent cell line. Using typical cell culture medium such as MEM  + 10%FCS. 

Thanks a lot.